in situ Tracking Water Oxidation Generated Lattice Strain Effects in Layered Double Hydroxides Nanosheets

doi:10.21203/rs.3.rs-2486537/v1

Download PDF

Article

in situ Tracking Water Oxidation Generated Lattice Strain Effects in Layered Double Hydroxides Nanosheets

https://doi.org/10.21203/rs.3.rs-2486537/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Layered double hydroxides (LDHs) have been identified as a potential catalyst for water oxidation, and it is recognized that they exhibit a dynamic and heterogeneous evolution of their lattice structure during their operation. In this study, we investigate the dynamic and heterogeneous evolution of LDHs during operation as a water oxidation catalyst using in situ electrochemical atomic force microscopy. Our results demonstrate that the lattice strain in LDHs triggers its heterogeneous structural dynamics at the nanoscale and has implications for the oxygen evolution reaction (OER) performance. The NiCo LDHs transforms to catalytically active NiCoO_x(OH)_2−x phase during operation, which produces compressive lattice strain and reversible tensile strain. The compressive strain along active edge sites of the nanosheets results in structural collapse and long-term degradation. Additionally, nanobubbles nucleate and grow at the electrocatalytic interfaces, leading to surface blockage and deterioration of catalytic efficiency. By engineering defects, we can precisely tune the strain and gas behavior during operation, leading to improved OER activity and stability among LDHs-based catalysts

Physical sciences/Materials science/Techniques and instrumentation/Microscopy/Atomic force microscopy

Physical sciences/Energy science and technology/Renewable energy/Hydrogen energy/Hydrogen fuel/Hydrogen storage

Water oxidation is a crucial component in various energy storage and conversion technologies, such as rechargeable metal-air batteries, water splitting devices, and carbon dioxide electrolyzers.¹ However, the slow kinetics of the oxygen evolution reaction (OER) results in a significant loss of energy, limiting overall efficiency.^2,3 While IrO₂ and RuO₂ have been utilized as efficient catalysts to overcome the kinetic barriers, their practical application is impeded by limited resources. Layered double hydroxides (LDHs) have been considered as promising non-precious OER catalysts in alkaline. A significant challenge in the development of improved LDH-based catalysts is understanding how the electrocatalytic interfaces evolve under realistic conditions and how this evolution affects OER efficiency.

In a variety of studies, the LDHs-based catalysts have been demonstrated to evolve with applied voltage, where the protons de-intercalate to form active (oxy)hydroxides species during OER.^4–7 The operando evolution changes crystalline structure of the material, generating lattice strain that could affect its electrocatalytic activity and stability.^8–11 Clearly, identifying induced strain effects during operation and understanding their influence on electrocatalytic performance is of fundamental importance for formulating design rules to fully utilize LDHs. However, limited information has been gained on the in situ behavior of strained LDHs under the operating conditions. Much less attention has been paid to studying the spatial strain evolution during operation that associated with the heterogeneous behavior of intrinsic disorder (e.g. edges, steps and defects)^12–15 and interparticle interactions^16,17.

In this study, we employ in situ electrochemical atomic force microscopy (EC-AFM) to track the structural dynamics of materials at the nanoscale under OER operation. Single-layered NiCo LDHs nanosheets were selected as the model system due to their well-defined geometry and impressive OER activity. By combining experimentally observed results and density functional theory (DFT) calculations, we show that water oxidation induces lattice strain on the nanosheets, leading to structural dynamics. Additionally, we monitor the operando evolution of defective and stacking nanosheets to understand how structural heterogeneity and material interactions affect operando dynamics. We observe heterogeneous strain effects and, through theoretical analyses, determine their origins and implications for electrocatalytic efficiency. Based on these results, we propose a modification strategy to optimize the OER performance of LDH-based catalysts by controlling strain effects and gas nucleation during operation.

Strain evolution of SL-NiCo LDHs nanosheets under operation

The SL-NiCo LDHs nanosheets was prepared via liquid exfoliation of the bulk precursor (see preparation details in Methods, Supplementary Fig. 1),^18,19 then dispersed on highly oriented pyrolytic graphite (HOPG), serving as the working electrode (WE). AFM measurement (Fig. 1b) shows flat hexagonal structures of thenanosheets, with an apparent single-layer height of 0.9 ± 0.2 nm (Supplementary Fig. 2),¹⁹ and an average diameter of 409.8 ± 5.4 nm (Supplementary Fig. 3). High angle annular dark field imaging scanning transmission electron microscopy (HAADF-STEM, Fig. 1c i) images and Energy Dispersive X-Ray spectroscopy (EDX, Supplementary Fig. 4) demonstrate that the single layers have uniform Ni, Co and O distributions. We collected scanning nanobeam electron diffraction (NBED) datasets of the area shown in Fig. 1c i, with distinct colors highlight different nanosheets (Fig. 1c ii). Corresponding non-negative matrix factorization (NMF) decomposition results correspond to the diffraction patterns oriented along the 001 axis, albeit azimuthally oriented in different orientations (Fig. 1c iii). This data thus demonstrates that SL-NiCo LDHs nanosheets have a well-defined long-range ordered structure in their ab plane.

Fig. 1d shows representative cyclic voltammetry (CV) of the electrode in 0.1 M KOH. A sharp precatalytic redox feature can be discerned in the CV curves, which corresponds to the transition of NiCo LDHs to catalytically active state prior to onset of the OER.²⁰ Under repetitive voltammetry cycles, the redox wave shifts cathodically and the peak integrated intensity increases (indicated by the red arrow from the 4^th cycle to the 32^nd cycle), meaning an activation process of the nanosheets towards more efficient charge transfer under operation.²¹ After the activation, a clear redox pair is observed at 470 mV and 378 mV vs. Ag/AgCl, respectively. Note that all electrochemical measurements in this work are performed in 0.1 M KOH electrolyte and all potentials are referenced against the Ag/AgCl electrode unless stated otherwise.

The changes of nanosheets with voltage were then monitored by in situ EC-AFM measurements, where operando AFM images of the electrode were acquired under a gradient bias (more details are shown in Supplementary Figs. 5-6). Fig. 1e shows the topographical evolution of a single SL-NiCo LDHs nanosheet. During anodic stepping, the nanosheet contracts as the bias reach 600 mV (ⅴ), and it expands reversibly to its initial state under cathodic stepping to 300 mV (ⅻ), as indicated by the dashed hexagon that refers to the initial size of the nanosheet. This corroborates the fine reversibility of the nanostructural transformation, and the reversible transition behaviors are repeatable under successively switching the redox bias (Supplementary Fig. 7). The evolving tendency in the potential range was quantitatively shown in Fig. 1f, where the compress ratio of the nanosheet compared to the initial state (1- A_p/A₀, A₀ and A_p are the surface areas extracted from the AFM image at open circuit (OC) and under different applied biases, respectively) is plotted as a function of bias. There is a clear correlation between the tendency for nanostructural transformation and redox state changes. The nanosheet compresses significantly as the potential steps over the oxidation peak of 513 mV (as shown in the initial CV curve, Fig. 1d), with the value being stable at 700 mV. Statistics on multiple nanosheets (Supplementary Fig. 8) show an average compress ratio of 12.5 ± 0.2% at 700 mV (Fig. 1f, insert). During backward stepping, the ratio decreases sharply until the bias falls below the reduction peak of 378 mV (as shown in the steady CV curve, Fig. 1d), with the value back to the initial non-contrast state. These results suggest that the phase transition of NiCo LDHs during OER should be responsible for its geometric deformation.

To further elucidate the underlying relations, we calculated the structural parameters of the as-prepared NiCo LDHs and two potential active oxidation phases (NiCoOOH and NiCoO₂) with DFT simulation (Fig. 1g). The results show that the metal-metal distances^22-24 decrease from 3.13 Å of NiCo LDHs to 3.00 Å (NiCoOOH) and 2.80 Å (NiCoO₂), suggesting a lattice compression process under electrocatalytic activation. Therefore, the contraction and expansion behaviors of nanostructure under operations should be the result of the in-plane lattice constant variation induced compressive or tensile strain. These results build the link between nanoscale structure dynamics and lattice strain under OER conditions. Furthermore, when the NiCo LDHs transit to NiCoOOH and NiCoO₂, the computational unit cell compresses by 8.2% and 20.1%, respectively. Our experimentally obtained compress ratio of 12.5 ± 0.2 % after activation locates in between, therefore, the potential catalytically active phase should be identified as NiCoO_x(OH)_2−x(0<x<2).

Compressive strain induces structural collapse

We note the existence of intrinsic line defects within partial nanosheets from the STEM images (Supplementary Fig. 9). To resolve the strain effect of defects under OER conditions, we monitored operando structural evolution of the nanosheet shown in Fig. 2a i, in which four line defects were observed (highlighted with the white arrows and labeled as 1, 2, 3 and 4). Under an oxidation bias of 650 mV, the nanosheet cracks into three pieces along defects 1, 2 and 3 (Fig. 2a ii), and the separated pieces reversibly expand to reconnect after a reduction process (Fig. 2a iii). The oxidation of the nanosheet is envisaged to start from edge sites of the line defects,²⁵ producing mechanical forces in many directions as indicated by the red arrows in Fig. 2a-ii. Eventually, the compressive strain across the defects ‘tear apart’ the nanostructure. We note that no crevice appears along defect 4, which could be the consequence of synergy forces. The tensile strain under reduction pulls the lattice in converse directions, thus the nanostructure recovers.

We then compared the OER thermodynamics of the edge and basal plane sites of NiCo LDHs via DFT calculations. The edge sites are identified to be the Ni sites at (1 1 0) facets and the basal plane sites are identified to be the O sites after removing an H atom at the (0 0 1) facet (Fig. 2b).²⁶ The optimized structures for all intermediates adsorbed on the Ni site and O site of NiCo LDHs are shown in Supplementary 11 and 12, respectively. The overpotential for Ni site (0.637 eV) is smaller than that for O site (0.969 eV) (Fig. 2c), suggesting that the edge sites are more active than the basal plane sites. This supports the claim that the oxidation of the nanosheet starts at edge sites.

Strikingly, the newly produced crevices during activation cannot be fully repaired. The crevices would leave in the nanostructure and become obvious under successive CV operations (Supplementary Fig. 12), indicating the structural collapse during operation. This should be responsible for catalyst deactivation in the long run.^27,28 It is worth mentioning that the structural collapse exposes additional active edge sites, which could explain the initial activation of the sample, as evidenced by the CV measurements. Overall, the intrinsic line defects in nanostructures have contradictory effects on electrocatalytic activity and stability. How to reconcile this contradiction and achieve an overall optimization is the key to any deliberate modification.

Electrolytically generated nanobubbles induce surface blockage

In addition to geometric evolution of the nanosheet, in Fig. 2a, we can easily observe nanospots appearing on the surface under OER and disappearing after reduction. The height profiles along the grey dashed line in Fig. 2a clearly demonstrate the height changes of the same region (Fig. 2d). Then the AFM-based nanomechanical measurement indicates that the nanospots have a low Young’s modulus (Fig. 2e). It means that these species are very soft, consistent with previously reported mechanical properties of bubbles.²⁹ Therefore, these species can be ascribed to nanobubbles that nucleate and grow on the surface of the catalyst as OER processes,^30-32 and they are able to dissolve into the electrolyte upon the application of reducing biases.^33,34 Interestingly, we note the formation of thin gas layers around the nanosheets during OER (Supplementary Fig. 13), known as micropancakes,^35,36 which is possibly generated due to the diffusion and accumulation of O₂ from the nanosheets to nearby HOPG.

The formation of nanobubbles during OER is envisaged to block surface active sites, leading to degraded OER efficiency. Fig. 2f shows the chronoamperometry measurement of the SL-NiCo LDHs nanosheets electrode at 900 mV. The current density exhibits periodic fluctuation. Under the same conditions, the evolution of microbubbles can be directly observed with an optical microscope (Supplementary Fig. 14). We included the operando changes of a microbubble in Fig. 2f to illustrate the correlation between gas behavior and fluctuating trends. The nucleation and growth of nanobubbles obstruct the diffusion of electrolyte into active sites, resulting in increasing current decay. The continued growth and fusion of nanobubbles lead to microbubbles, and once reaching a critical size, the bubbles can detach from the electrode surface, making the blocked active sites re-accessible. Then, the current density can then jump back. The OER activity exhibits significant degradation after long-term CV operation, which should attribute to the accumulation of nanobubbles over the electrode surface (Supplementary Fig. 15).

Relaxation of strain induces wrinkles

We now turn to the operando evolution of stacking nanosheets to explore potential interactions during operation. Fig. 3a-ⅰ displays stacking nanosheets with pyramidal steps. Considerable wrinkles were observed after performing CVs (Fig. 3a-ⅱ) and they grow laterally and horizontally as the CV number increases (Fig. 3a-ⅲ). The growth tendency is directly shown in the corresponding height profiles (Fig. 3b). To gain further insight into the wrinkle structure, we compared the nanomechanical properties of wrinkles and planar regions using AFM-based force spectroscopy.^37,38 Force−separation curves (Fig. 3c) can be obtained by approaching the tip on the selected points of plane and wrinkle (white and black cross in Fig. 3a-ⅲ, respectively). The approaching curve to the plane (blue) is a classical one showing no detected long-range repulsive force in A-B segment, until the tip the tip reaches the sample surface, then the force increases linearly until the Z position of the modulation reaches the max force setpoint (B-C segment). In comparison, a clear kink is observed in the curves recorded on a wrinkle (red). The irregular increase of the force in the b-c segment should ascribe to the indentation into the wrinkle, made by the tip. The following decrease of force possibly results from the wrinkle deformation that can release partial force (c-d segment). Combined this indicates the presence of buckling delaminated wrinkle structure, and reveals the intrinsic flexibility of the SL-NiCo LDHs nanosheets.

To understand the wrinkling mechanism, we resolved operando topographical evolution of the stacking SL-NiCo LDHs nanosheets shown in Fig. 4a, with the detailed AFM images under different biases displayed in Supplementary Fig. 16. The stages exhibiting obvious nanostructural transitions are shown in Fig. 4a-e ⅰ. The evolving mechanism for each stage is schematically shown in Fig. 4a-e ii and demonstrated in the following:

a) Initially, a SL-NiCo LDHs nanosheet with defects (top-layer, L_t) vertically stacks on a well-defined hexagonal nanosheet (bottom-layer, L_b).

b) At 600 mV, L_t cracks as indicated by the white arrows. L_b shows a tiny contraction as signified by the slight separation from the neighboring nanosheets (indicated by the red arrow). The distinct compressive strain of two layers suggests their asynchronous oxidation, where L_b insufficiently oxidizes compared with L_t. This most likely because the coverage of L_t obstructs electrolyte diffusion to underneath L_b, resulting in impeded OER processes.

c) At the following 650 mV, the crevice in L_t narrows and considerable wrinkles occur. L_b continues to contract as signified by the larger separation from the neighboring nanosheets, as well as the formation of crack in L_b (indicated by the red arrows). We propose that the continued oxidization of L_b induces biaxial compressive strain of L_bthat can be transmitted to L_t perpendicular to the strain direction by frictional forces. Then the relaxation of biaxial compression enabled the buckling delamination to form wrinkles in L_t.³⁹ Importantly, the wrinkles are prone to derive from the edges and merge at a junction to form a “Y” shape or “T” shape,⁴⁰ which agrees well with the energetically favorable pathway in biaxial wrinkling.

d) Under the reduction bias of 400 mV, in L_t, the wrinkles network disappears, and the crevices reappear. Meanwhile, L_b expands to recontact the neighboring nanosheets. Similarly, the reduction of L_b induces biaxial tensile strain, and its relaxation driving localized unfolding of the wrinkles in L_t.

e) Further reduction to 300 mV results in a denser wrinkles network on L_t, while no noticeable change was observed in L_b. This is where L_t is reduced to induce tensile strain. However, due to the constraint effect of the L_b,⁴¹ the strain can be released in situ at L_t, eventually developing into the dense wrinkles network.

The transformation trends are repeatable (Supplementary Fig. 17), supporting the validity of the proposed electrode process. These findings illustrate the interaction between SL-NiCo LDHs nanosheets under working conditions, in which several characteristics could impact the OER efficiency: ⅰ) The wrinkles expand under continuous operation due to the accumulation of the strain release (as evidenced in Fig.3 a),⁴⁰ resulting in volume expansion lifting the top-layer (Supplementary Fig. 18). This phenomenon could increase the instability of the electrocatalytic interfaces, leading to attenuation of catalysts under long-term operation. ii) The presence of wrinkles tensile the basal plane of nanosheets, which have previously been reported to tune surface adsorption free energy⁴² and electronic transport properties⁴³ of layered crystals, possibly activating and optimizing basal plane sites of SL-NiCo LDHs nanosheets towards OER.

Strain control of catalysts to modify electrocatalytic performance

Based on the above understanding, two key factors are suggested to modify OER performance of the SL-NiCo LDHs catalyst: i) Controlling strain to preserve beneficial strain during the electrocatalytic processes and restrain mechanical collapse and volume expansion. ii) Tuning interfacial affinity to restrain nucleation or accelerate the release of surface nanobubbles. Defect engineering has previously been proven to be an effective method to these aims. With abundant and uniform defects in nanomaterials, it is envisaged that the strain created in many directions should offset each other or be relaxed by the defects, and the affinity between electrode, electrolyte and gas could also be modified to promote mass diffusion, thus allowing for optimized OER performance.^44,45 As a proof of concept, we introduce uniform defects on the SL-NiCo LDHs nanosheets by Ar plasma etching (see details in Methods), then performed in situ EC-AFM measurements to compare the effects of defects to OER interfacial dynamics.

After plasma irradiation, the surface root mean square (RMS, donated as S_q) roughness increases from initial 0.08 nm (Fig. 5a i) to 0.10 nm (Fig. 5a ii), suggesting that a defective surface has formed on the plasma-treated SL-NiCo LDHs (PSL-NiCo LDHs) nanosheets. Upon stepping to 650 mV, the SL-NiCo LDHs nanosheets exhibit contraction, crack, and nanobubbles as indicated by the white arrows, black arrows and red circles, respectively (Fig. 5c). While these dynamics are negligible on PSL-NiCo LDHs nanosheets under the same conditions (Fig. 5d), and the wrinkling phenomenon does not occur on the stacking PSL-NiCo LDHs nanosheets (Fig. 5e). These findings provide direct proof that uniform defects can restrain mechanical deformation in nanostructure and obstruct the formation of O₂ nanobubbles at the interfaces.

Next, we examined the effects of uniform defects on the catalytic OER activity of SL-NiCo LDHs nanosheets. Fig. 5f shows representative linear sweep voltammograms (LSV) for the as-prepared electrode before and after plasma treatment. As expected, the PSL-NiCo LDHs nanosheets exhibit lower OER overpotential compared with SL-NiCo LDHs nanosheets, and the Tafel slope (Fig. 5g) of PSL-NiCo LDHs (53.91 mV dec⁻¹) is lower than SL-NiCo LDHs (73.66 mV dec⁻¹). The electrochemically active surface area (ECSA) increases after the plasma irradiation (Supplementary Fig. 19). In addition, the PSL-NiCo LDHs exhibits a higher and more stable current density at a chronopotentiometry potential of 900 mV (Fig. 5h), suggesting better stability compared with SL-NiCo LDHs. It was observed that the surface of PSL-NiCo LDHs nanosheets remains flat after performing 8000 cycles of CVs. The OER activity exhibits less degradation (Supplementary Figure 20) compared with that of SL-NiCo LDHs (Supplementary Fig. 15). These results confirm the notable OER activity and stability enhancement after plasma treatment, which should be attributed to the modification of the operando strain and interfacial affinity by the uniform defects.

In summary, we have visualized the heterogeneous strain effects of SL-NiCo LDHs nanosheets under OER conditions using in situ EC-AFM, and then theoretically described the origins and strain-performance relationships. During operation, the SL-NiCo LDHs nanosheets undergo operando evolution to form catalytically active NiCoO_x(OH)_2−x phase, which induces lattice strain to compress nanosheets. This is reversible under reduction process. The compressive strain preferentially occurs along the intrinsic line defects in the nanosheets, leading to structural collapse that are correlated to initial activation and long-term degradation. The electrolytically generated nanobubbles accumulate on the surface of nanosheets during OER, resulting in surface blockage that could reduce the electrocatalytic efficiency. Moreover, the interacting nanosheets induce biaxial strain, driving the formation of buckling delaminated wrinkles, which brings about volume expansion and basal plane modification that possibly associate with degradation and activation of catalysts, respectively. On these bases, defect engineering is suggested and confirmed as an effective method to optimize the OER performance of the catalysts by tuning the strain effects and gas behavior during operation. Our findings advance the understanding of the strain effects under realistic conditions and provide insight into degradation and/or activation mechanisms at the nanoscale, which helps guide the rational design of LDHs-based OER electrocatalysts. Furthermore, combining in situ EC-AFM method and theoretical approach to explicitly demonstrate how the lattice strain triggers the structural dynamics at the nanoscale and the implications for electrocatalytic performance of the materials is broadly applicable to a wide range of heterogeneous electrocatalysis processes beyond OER.

Synthesis of bulk NiCo LDHs. In a typical hydrothermal procedure, 0.5 M nickel nitrate (Ni(NO₃)₂·6H₂O, 98%, Alfa Aesar)), 0.5 M cobalt nitrate (Co(NO₃)₂·6H₂O, 98%, Alfa Aesar), 0.25 M sodium dodecyl sulfate (SDS, Fisher Scientific), and 1 M hexamethylenetetramine (HMT, Alfa Aesar) stock solutions in water were prepared. Then the Ni(NO₃)₂·6H₂O (3 mL), Co(NO₃)₂·6H₂O (1 mL), SDS (40 mL), and HMT (12 mL) solution were mixed in a 200 mL Teflon vessel with 44 mL deionized Milli-Q water. The sealed container was kept at 120°C for 24 h, then cooled down to room temperature naturally. The precipitates were washed and centrifuged with water and ethanol several times and dried overnight.

Synthesis of SL-NiCo LDHs. Specifically, 15 mg bulk NiCo LDHs was dispersed in 30 mL formamide and maintained at 40°C for 5 days to drive the exfoliation process. The suspension was centrifuged at 2,000 rpm for 30 min, and the as-obtained supernatant was transferred into a clean tube and centrifuged at 10,000 rpm for 30 min. Then the sediments were washed and centrifuged with water and ethanol several times (13,000 rpm for 30 min), and the product was finally suspended in 2 mL ethanol.

Defect engineering on SL-NiCo LDHs. 30 µL SL-NiCo LDHs nanosheets suspension was dispersed on a freshly cleaved HOPG surface, subsequently heating at 180°C for 60 min. The SL-NiCo LDHs/HOPG samples were exposed to Ar plasma for 1 min in a plasma reactor (commercial 13.56 MHz RF source), with a power of 300 W and pressure of 40 Pa.

AFM characterization. AFM images were acquired on a Multimode Nanoscope VIII (Bruker, Santa Barbara, USA) with a ScanAsyst-fluid probe (Bruker). In situ measurements were carried out in EC-ScanAsyst mode with force control. Quantitative mechanical measurements were conducted with using PeakForce Quantitative NanoMechanics (PF-QNM) Mode. The tip radius was calibrated using a tip characterizer sample and a tip qualification function, and defection sensitivity was calibrated by a PF-QNM ramp on HOPG in the electrolyte, then the spring constant was calibrated by thermal tuning. A passion ratio of 0.5 was used here. The phase profile was acquired in tapping mode. The force curves at points of interest were collected using a “point and shoot” module in EC-ScanAsyst. All images were further processed and analyzed by SPIP.

Other material characterization. STEM-HAADF was performed using a 200 kV FEI Talos F200X analytical STEM equipped with a TWIN lens, an X-FEG electron source. NBED patterns of individual (and multiple stacked) sheets were collected using a beam with a convergence angle of 0.6mrad. The data was subsequently analyzed using non-negative matrix factorization. Finally, STEM-EDX data was collected on the same microscope using the ChemiSTEM/SuperX G1 setup. Data was analyzed and visualized using the HyperSpy package. X-ray diffraction analysis (XRD) was carried on a Rigaku Smart Lab diffractometer, using a Cu source and a convergent beam mirror (Cu Kα1 radiation, λ = 1.540593 Å). The Fourier transform infrared spectroscopy (FTIR) was measured with the Cary 630 FTIR spectrometer (Agilent) with the dTGS detector.

Electrochemical characterization. The classical electrochemical measurements were performed in a homemade cell (the electrode exposed area is 0.56 cm²) with a three-electrode system using an electrochemical workstation (CHI 760E). The sample prepared on HOPG was used as working electrodes, and a carbon rob and an Hg/HgO electrode were used as counter electrode and reference electrode, respectively. The potentials were reported against the saturated Ag/AgCl electrode. All measurements were performed at 0.1 M KOH.

Computational method. All DFT calculations employed the Vienna Ab initio Simulation Package (VASP) together with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional^46–48. To generate an accurate adsorption geometry, the van der Waals (vdW) interactions were considered by using Grimme’s semiempirical DFT + D3 scheme⁴⁹. The Hubbard-U correction was used to describe the local d-electrons of Ni and Co in SL-NiCo LDHs. The U-J values of Ni and Co are 3.8 and 4.0 eV, respectively⁵⁰. A cutoff energy of 450 eV was set in all calculations. For structural optimizations, the used Brillouin zone sampling was (9×9×1) for (001) surface and (5×1×1) for (110) surface of SL-NiCo LDHs⁵¹. The convergence criterion of energy difference was set to 10^− 4 eV for structural optimization, and 10^− 5 eV for static calculations. The atomic positions were relaxed until the maximal force on each atom was smaller than 0.02 eV/Å. The following mechanism of OER was adopted:

\({\text{H}}_{2}\text{O}+ \text{} \to \text{}\text{O}\text{H}+{\text{H}}^{+}+{\text{e}}^{-}\)	(1)
\(OH \to O+{\text{H}}^{+}+{\text{e}}^{-}\)	(2)
\({H}_{2}O+O \to OOH+{\text{H}}^{+}+{\text{e}}^{-}\)	(3)
\(OOH \to +{O}_{2}+{\text{H}}^{+}+{\text{e}}^{-}\)	(4)
The * indicates the active site in SL-NiCo LDHs, and OH, O, *OOH are the intermediate species on the active sites. The Gibbs free energies of each step are calculated by the following formula:

\(\varDelta {G}_{1}={E}_{OH}+1/2{E}_{{H}_{2}}-{E}_{}-{E}_{{H}_{2}O}+\varDelta ZPE-T\varDelta S\)	(5)
\(\varDelta {G}_{2}={E}_{O}+1/2{E}_{{H}_{2}}-{E}_{OH}+\varDelta ZPE-T\varDelta S\)	(6)
\(\varDelta {G}_{3}={E}_{OOH}+1/2{E}_{{H}_{2}}-{E}_{O}-{E}_{{H}_{2}O}+\varDelta ZPE-T\varDelta S\)	(7)
\(\varDelta {G}_{4}=4.92-\varDelta {G}_{1}-\varDelta {G}_{2}-\varDelta {G}_{3}\)	(8)

\({E}_{*}\) , \({E}_{*OH}\), \({E}_{*O}\), \({E}_{*OOH}\), represent the total energy of intermediate species and \({E}_{{H}_{2}}\), \({E}_{{H}_{2}O}\) indicate the total energy of H₂ and H₂O. The electrocatalytic activity at finite temperature was considered by introducing the correction of Zero-Point Energy (ZPE) and entropy change⁵².

Acknowledgments

We gratefully acknowledge the financial support from the Danish Council for Independent Research (9040-00219B), European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement SENTINEL (Grant No. 812398).

Additional information

Competing interests: The authors declare no conflict of interests.

Huang, Z.-F. et al. Tuning of lattice oxygen reactivity and scaling relation to construct better oxygen evolution electrocatalyst. Nat. Commun. 12, 3992 (2021).
Tahir, M. et al. Electrocatalytic oxygen evolution reaction for energy conversion and storage: A comprehensive review. Nano Energy 37, 136–157 (2017).
Song, J. et al. A review on fundamentals for designing oxygen evolution electrocatalysts. Chem. Soc. Rev. 49, 2196–2214 (2020).
Zhao, S. Insight into structural evolution, active sites, and stability of heterogeneous electrocatalysts. Angew. Chem. Int. Ed. 134, e202110186 (2022).
Selvam, N. C. S., Du, L., Xia, B. Y., Yoo, P. J. & You, B. Reconstructed water oxidation electrocatalysts: The impact of surface dynamics on intrinsic activities. Adv. Funct. Mater. 31, 2008190 (2021).
Ding, H., Liu, H., Chu, W., Wu, C. & Xie, Y. Structural transformation of heterogeneous materials for electrocatalytic oxygen evolution reaction. Chem. Rev. 121, 13174–13212 (2021).
Zhao, S., Yang, Y. & Tang, Z. Insight into structural evolution, active sites, and stability of heterogeneous electrocatalysts. Angew. Chem. Int. Ed. 134, e202110186 (2022).
Wang, H. et al. Direct and continuous strain control of catalysts with tunable battery electrode materials. 354, 1031–1036 (2016).
Xu, G.-L. et al. Native lattice strain induced structural earthquake in sodium layered oxide cathodes. Nature Communications 13, 436 (2022).
Liu, T. et al. Origin of structural degradation in li-rich layered oxide cathode. Nature 606, 305–312 (2022).
Luo, M. & Guo, S. Strain-controlled electrocatalysis on multimetallic nanomaterials. Nature Reviews Materials 2, 17059 (2017).
Takahashi, Y. et al. High-resolution electrochemical mapping of the hydrogen evolution reaction on transition-metal dichalcogenide nanosheets. Angew. Chem. Int. Ed. Engl. 59, 3601–3608 (2020).
Wang, Z. et al. Controllable etching of mos2 basal planes for enhanced hydrogen evolution through the formation of active edge sites. Nano Energy 49, 634–643 (2018).
Pfisterer, J. H. K., Baghernejad, M., Giuzio, G. & Domke, K. F. Reactivity mapping of nanoscale defect chemistry under electrochemical reaction conditions. Nat. Commun. 10, 5702 (2019).
Mariano Ruperto, G., McKelvey, K., White Henry, S. & Kanan Matthew, W. Selective increase in co2 electroreduction activity at grain-boundary surface terminations. Science 358, 1187–1192 (2017).
Kang, M. et al. Simultaneous topography and reaction flux mapping at and around electrocatalytic nanoparticles. ACS Nano 11, 9525–9535 (2017).
Ustarroz, J. et al. Mobility and poisoning of mass-selected platinum nanoclusters during the oxygen reduction reaction. ACS Catalysis 8, 6775–6790 (2018).
Ida, S., Shiga, D., Koinuma, M. & Matsumoto, Y. Synthesis of hexagonal nickel hydroxide nanosheets by exfoliation of layered nickel hydroxide intercalated with dodecyl sulfate ions. Journal of the American Chemical Society 130, 14038–14039 (2008).
Song, F. & Hu, X. L. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis. Nat. Commun. 5 (2014).
Deng, J. et al. Morphology dynamics of single-layered ni (oh)2/niooh nanosheets and subsequent fe incorporation studied by in situ electrochemical atomic force microscopy. Nano Lett. 17, 6922–6926 (2017).
Schneiderová, B. et al. Nickel-cobalt hydroxide nanosheets: Synthesis, morphology and electrochemical properties. J. Colloid Interface Sci. 499, 138–144 (2017).
McBreen, J., O'Grady, W., Pandya, K., Hoffman, R. & Sayers, D. J. L. Exafs study of the nickel oxide electrode. Langmuir 3, 428–433 (1987).
Guay, D. et al. In-situ time-resolved exafs study of the structural modifications occurring in nickel oxide electrodes between their fully oxidized and reduced states. J. electroanal. chem. interfacial electrochem. 305, 83–95 (1991).
Dionigi, F. et al. In-situ structure and catalytic mechanism of nife and cofe layered double hydroxides during oxygen evolution. Nat Commun 11, 2522 (2020).
Chen, R.-r., Mo, Y. & Scherson, D. A. In situ atomic force microscopy imaging of electroprecipitated nickel hydrous oxide films in alkaline electrolytes. Langmuir 10, 3933–3936 (1994).
Bi, Y. et al. Understanding the incorporating effect of co2+/co3 + in nife-layered double hydroxide for electrocatalytic oxygen evolution reaction. J. Catal. 358, 100–107 (2018).
Xie, J. et al. Intralayered ostwald ripening to ultrathin nanomesh catalyst with robust oxygen-evolving performance. Adv. Mater. 29, 1604765 (2017).
Dette, C., Hurst, M. R., Deng, J., Nellist, M. R. & Boettcher, S. W. Structural evolution of metal (oxy)hydroxide nanosheets during the oxygen evolution reaction. ACS Appl. Mater. Interfaces 11, 5590–5594 (2019).
Zhao, B. et al. Mechanical mapping of nanobubbles by peakforce atomic force microscopy. Soft Matter 9, 8837–8843 (2013).
Gu, J. Y., Cai, Z. F., Wang, D. & Wan, L. J. Single-molecule imaging of iron-phthalocyanine-catalyzed oxygen reduction reaction by in situ scanning tunneling microscopy. ACS Nano 10, 8746–8750 (2016).
Wang, X., Cai, Z. F., Wang, D. & Wan, L. J. Molecular evidence for the catalytic process of cobalt porphyrin catalyzed oxygen evolution reaction in alkaline solution. J. Am. Chem. Soc. 141, 7665–7669 (2019).
Wang, X. et al. In†࿽situ scanning tunneling microscopy of cobalt-phthalocyanine-catalyzed co2 reduction reaction. Angew. Chem. Int. Ed. 59, 16098–16103 (2020).
Luo, L. & White, H. S. Electrogeneration of single nanobubbles at sub-50-nm-radius platinum nanodisk electrodes. Langmuir 29, 11169–11175 (2013).
German, S. R., Chen, Q., Edwards, M. A. & White, H. S. Electrochemical measurement of hydrogen and nitrogen nanobubble lifetimes at pt nanoelectrodes. J. Electrochem. Soc. 163, H3160-H3166 (2016).
An, H., Liu, G. & Craig, V. S. J. Wetting of nanophases: Nanobubbles, nanodroplets and micropancakes on hydrophobic surfaces. Adv. Colloid Interface Sci. 222, 9–17 (2015).
Zhang, X. H., Maeda, N. & Hu, J. Thermodynamic stability of interfacial gaseous states. J. Phys. Chem. B 112, 13671–13675 (2008).
An, H. et al. Graphene nanobubbles produced by water splitting. Nano Lett. 17, 2833–2838 (2017).
Wang, Y., Wang, H., Bi, S. & Guo, B. Nano-wilhelmy investigation of dynamic wetting properties of afm tips through tip-nanobubble interaction. Sci. Rep. 6, 30021 (2016).
Jiang, T., Huang, R. & Zhu, Y. Interfacial sliding and buckling of monolayer graphene on a stretchable substrate. Adv. Funct. Mater. 24, 396–402 (2014).
Zhang, K. & Arroyo, M. Understanding and strain-engineering wrinkle networks in supported graphene through simulations. Journal of the Mechanics and Physics of Solids 72, 61–74 (2014).
Wan, J. et al. Ultra-thin solid electrolyte interphase evolution and wrinkling processes in molybdenum disulfide-based lithium-ion batteries. Nat. Commun. 10, 3265 (2019).
Li, H. et al. Activating and optimizing mos2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies. 15, 48–53 (2016).
Kushima, A., Qian, X., Zhao, P., Zhang, S. & Li, J. Ripplocations in van der waals layers. Nano Lett. 15, 1302–1308 (2015).
Wang, Y. et al. Layered double hydroxide nanosheets with multiple vacancies obtained by dry exfoliation as highly efficient oxygen evolution electrocatalysts. Angew. Chem. Int. Ed. Engl. 56, 5867–5871 (2017).
Tao, L., Duan, X., Wang, C., Duan, X. & Wang, S. Plasma-engineered mos2 thin-film as an efficient electrocatalyst for hydrogen evolution reaction. Chem. Commun. 51, 7470–7473 (2015).
Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Perdew, J. P. et al. Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 46, 6671–6687 (1992).
Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (dft-d) for the 94 elements h-pu. J. Chem. Phys. 132, 154104 (2010).
Bi, Y. et al. Understanding the incorporating effect of co2+/co3 + in nife-layered double hydroxide for electrocatalytic oxygen evolution reaction. J. Catal. 358, 100–107 (2018).
Monkhorst, H. J. & Pack, J. D. Special points for brillouin-zone integrations. Phys. Rev. B 13, 5188–5192 (1976).
Zhu, Y.-A., Chen, D., Zhou, X.-G. & Yuan, W.-K. Dft studies of dry reforming of methane on ni catalyst. Catal. Today 148, 260–267 (2009).

There is NO Competing Interest.

SupplementalInformation.docx
Supplemental Information

Download PDF

Version 1

posted

You are reading this latest preprint version

\({\text{H}}_{2}\text{O}+ \text{} \to \text{}\text{O}\text{H}+{\text{H}}^{+}+{\text{e}}^{-}\)	(1)
\(OH \to O+{\text{H}}^{+}+{\text{e}}^{-}\)	(2)
\({H}_{2}O+O \to OOH+{\text{H}}^{+}+{\text{e}}^{-}\)	(3)
\(OOH \to +{O}_{2}+{\text{H}}^{+}+{\text{e}}^{-}\)	(4)
The * indicates the active site in SL-NiCo LDHs, and OH, O, *OOH are the intermediate species on the active sites. The Gibbs free energies of each step are calculated by the following formula:

in situ Tracking Water Oxidation Generated Lattice Strain Effects in Layered Double Hydroxides Nanosheets

Status:

Version 1

Abstract

Figures

Introduction

Results And Discussion

Conclusion

Methods

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1