Low Cost Co3O4 &amp; Neem Leaves Derived Carbon Composite: High-Performance Oxygen Reduction Electro-catalyst for AEMFC

doi:10.21203/rs.3.rs-3893772/v1

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Low Cost Co₃O₄ & Neem Leaves Derived Carbon Composite: High-Performance Oxygen Reduction Electro-catalyst for AEMFC

https://doi.org/10.21203/rs.3.rs-3893772/v1

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The catalyst development for the oxygen reduction reaction (ORR) which is an important part of metal-air batteries and fuel cells, is immensely profitable. Along with the aim of development, cost-effectiveness is a needful parameter that gives competitive aspects of the product in the market of energy storage and conversion field. Here, we report the co-precipitation synthesis of cost-effective Co₃O₄ nanoparticles with the neem leaves-derived carbon (NC) as an efficient oxygen reduction catalyst resulting in a scalable alternative. The structural, phase analysis, thermo-gravimetric, and electrochemical analysis are studied by imposing the pertinent experimental techniques of the prepared catalyst Co₃O₄@NC. Moreover, the affirmation of the pure phase Co₃O₄@NC has been done by the oxidation state analysis by X-day photoelectron microscopy. Further, the performance of the fuel cell was tested with distinct loading of catalyst in which for equal loadings of standard platinum-based Ptc 40% and with replacing with Co₃O₄@NC. The open circuit potential of the Ptc 40 wt% based cell supply is 0.957 and for Co₃O₄@NC is 0.925 which is just 3.34% less than Ptc 40%. The low cost and highly active oxygen reduction reaction (ORR) cathode Co₃O₄@NC has been demonstrated in anion-exchange membrane fuel cell (AEMFC) with single-cell assembly.

Neem leaf carbon

Biomass- carbon

Hydrogen

Electrolysis

Global warming is increasing day by day due to the use of fossil fuels in the energy sector.[1] A fuel cell is a promising technology for producing electricity and producing zero emissions. In fuel cell technology many researchers are focused on the platinum-free electro-catalyst as the alternative solution for reducing dependency on the foreign company.[2]

Natural waste can be used to develop new materials for various applications. Researchers have synthesized carbon material from natural waste for use in PEM fuel cells, batteries, super-capacitors, and other applications. This approach is gaining popularity as it helps to reduce waste and promote sustainable development.

PEM Fuel is a promising candidate for the application of automobiles, electricity generator sets, etc. Fuel cells have high current density and durability also good compared to other technologies, in battery charging and discharging is the process, fuel cells supply the fuel continuously it will get the electricity till the fuel supply. In the fuel cell, the two reactions occur at the Cathode side Oxygen reduction reaction (ORR) and anode side Hydrogen Evolution reaction (HER). ORR reaction is very important for the fuel cells and future upcoming energy devices.[3] ORR is the most important reaction in the field of electrochemistry, this reaction is sluggish and has lots of limitations for fuel cell application. However, the kinetics of the cathode ORR is a very slow reaction.[4] Platinum-based noble metal-based electrocatalyst for improving the ORR kinetics; however, due to the very high cost as compared to other precious metal, stability and durability is also not good, and many more challenges for this platinum catalyst.[4] Therefore there is a very urgent need to develop platinum platinum-free electro-catalyst for the PEM fuel cell application.

Cost-effective Cobalt oxide (Co₃O₄) is a highly efficient alternative to standard platinum based electro-catalyst with nearly similar performance, thus it has gained the attention of researchers.[5, 6] Yongye Liang et.al worked on ORR activity of Co₃O₄/N-doped graphene electrocatalyst with nearly similar activity in the catalysis process which makes it a potential and important electrode for PEM fuel cells.[6] Hydrothermally synthesized nano-spinel Co₃O₄ additive was tested for microbial fuel cells to enhance the performance of activated carbon air cathode.[7] The graphene oxide based Co₃O₄ was synthesized by ultrasonication method and was tested the performance in anion exchange membrane fuel cell (AEMFC) with the comparison of Ptc 20% in which the current densities for oxygen reduction reaction (ORR) was found 4.30 mA/cm² for Cobalt oxide and for Ptc 20% was 4.62 mA/cm².[5] These reports suggest the cobalt oxide and its combination with carbon based additives to improve the activity of the electrocatalysis for ORR and needs to focus on cost-effective carbon additives. Carbon is the most abundant material is available in nature and this carbon has the high surface area, chemical inertness and synthetically tunable electrical, thermal and optical properties which has the potential to save the fossil fuels.[8]

We have synthesized the composite of dead neem leaves carbon and the cobalt oxide (Co₃O₄). After the synthesis of neem carbon[8] and the with the addition of KOH/ Co (NO₃)₂ the combination of microporous carbon and Co₃O₄ obtained.[9, 10] based catalyst is the high efficient catalyst that enable and durable electrode fabrication for the fuel cell application.[11] Cobalt oxide is the widely used in the ORR catalyst in alkaline, microbial and PEM fuel cells.[12–14] We have checked the half-cell reaction the cobalt coated carbon gives us the 0.84 v and platinum catalyst 40wt% is 0.98V, approximately our material gives the performance nearest to commercial material. Half wave potential also Co based material is 0.695 V and commercial material Ptc gives us the 0.839 V.

We have checked in to the feasibility in to fuel cell testing Anode side used the ptc material and cathode side (ORR) used the Co₃O₄ with neem carbon (Co₃O₄@NC) based material for different loading. We get the power density almost similar to the commercial Ptc 40 wt%. Durability and material consistency is also similar to the commercial material. This obtained platinum free electro catalyst have showed the better ORR kinetics in the fuel cell application.

Materials and Chemicals: Neem tree leaves collected from Savitribai Phule Pune University campus. Potassium hydroxide (KOH) and Cobalt Nitrate Co(NO₃)₂ was purchased from Sigma -Aldrich. The platinum catalyst was purchased from Alfa Aesar. All the chemicals were used in without any extra purification or modification. For the fabrication of anion exchange membrane fuel cell (AEMFC), the gas diffusion layer (GDL: carbon paper) were procured form the SIGRACET. The anion exchange membrane was purchased from the FuMA-Tech GmbH.

Synthesis of carbon by Neem carbon

conversion of neem leaves to the porous carbon was carried out by the process of thermal decomposition. Initially, neem leaves were washed by distilled water (DI) and kept it overnight in an oven at 70^oC to remove the moisture. Later, dry leaves were crushed to fine powder and heated it in tube furnace at 900^oC (temperature raise by 10 ^oC minute^− 1) for 5 hours in an inert atmosphere (argon gas).

Activation of neem carbon & synthesis of Co3O4@NC:

Neem carbon was chemically activated using alkali compound such as potassium hydroxide (KOH) as it is a profound method to increase the surface area.[15, 16] The ratio of the KOH to neem carbon was fixed to 1:4 (g/g). The combination of KOH and neem carbon was dissolved in distilled water along with the ultra-sonication to achieve uniform dispersion[3]. Later, the collected KOH treated neem leaves powder was dried in vacuum oven at 100º C for 12 hours. To achieve the porous carbon from the source of neem leaves, carbonization process carried out under inert environment. The carbonization process carried out by heating the neem leaves in tube furnace at 900^oC (5^oC minute of temperature step) for 1 hour in argon gas and cooled down to room temperature. Later, the collected powder washed with distilled water and dried at 85 ^oC. However, to make the composite of Co₃O₄ with carbon derived by neem leaves, Co(NO₃)₂ and neem carbon taken with ratio of 4:1 & dissolved in DI water. The solution containing Cobalt and neem carbon heated at 180 ^oC for 4 hours in a hydrothermal reactor and after natural cooling down, precipitate of Co₃O₄@neem carbon (Co₃O₄@NC) was collected and dried at 85 ^oC. As synthesized composite-Co₃O₄@NC, used for characterization and application without any extra treatments. The obtained product was removed next day and this KOH activated carbon grind it sore in to the moisture free glass bottle. The complete synthesis process including the preparation of activated neem-carbon and its combination with Co₃O₄ has displayed in Scheme 1.

Characterizations

The high resolution transmission electron microscopy (HRTEM) analysis was carried out by dispersing 1 mg of the powdered sample in 5 µl was drop coated on a TEM grid wad dried under IR lamp and analyzed using FEI, TECNAI G2 F20 instrument operated at an accelerated voltage of 200 kv (C_s = 0.6 mm, resolution 1.7A^o. For the Surface Area and Pore Size Measurement by Gas Sorption by surface analyzer using Quantachrome Brunauer-Emmett-Teller (BET) surface area analysis is the multi- point measurement of an analyte`s specific surface area (m²/g), 230 V, 50HZ, 1100 VA, X-ray diffraction (XRD) analysis, Bruker D8 Advanced X-ray diffractometer at room temperature using cu Kα radiation (λ = 1.5406 Å) was used. The XRD scanning ranges from 10^o to 80^o with scan speed 0.5^o min^− 1 and step size of 0.01^o in 2θ.Thermogravimetric analysis (TGA) was carried out by using a SDTQ600 TG-DTA analyzer. The temperature ramp for the TGA instrument was 10^oC min^− 1 under the air environment. X – ray photoelectron spectroscopy (XPS) analysis was carried using a VG Microtech Multilab ESCA 3000 spectrometer attached with a Mg Kα –X-ray source (h_v =1.2536 keV) instrument. Furthermore, the loading of the Membrane Electrode Assembly (MEA) for Electrode making, Thermal Gravimetric Analysis instrument is very essential for the weight percentage calculation. KOH activated carbon and further synthesis with cobalt oxide (Co₃O₄@NC) carbon is testing form 50⁰C to 900⁰C in Oxygen environment. In TGA KOH activated carbon got 34 weight percent and Cobalt activated carbon got the 66 weight percent metal is present.

3.1 Structural properties of activated neem carbon (NC) and Co₃O₄@NC: Structural properties of the carbon and the hybrid system of Co₃O₄@C were achieved by X-ray diffraction (XRD) pattern. Fig. SI.1 shows the XRD pattern of the carbon and Fig. 1(a) shows the XRD pattern of hybrid Co₃O₄@NC. The observed sharp diffraction peaks positioned for Co₃O₄@NC at 19.17, 23.71, 37.08, 44.25, 59.38, and 65.16 corresponds to the planes (111), (002), (220), (311), (400), (422), and (440), results in high crystallinity. The XRD pattern matched with the JCPDS No.: 073-1701 representing the cubic spinel structure of Co₃O₄. The facile and trustworthy technique to determine the crystalline size of the nanomaterial is using Debye-Scherrer equation. The crystallite size evaluated by Debye-Scherrer equation given below:

$$\varvec{D}=\frac{\varvec{k} \varvec{\lambda }}{\varvec{B} \mathbf{c}\mathbf{o}\mathbf{s}\left(\varvec{\theta }\right)}$$

Where, k is shape factor (0.89), ${\lambda }$ corresponds to wavelength of the incident x-ray (1.54 Å), B corresponds to the full width half maxima (FWHM) and $\theta$ corresponds to the half angle of 2$\theta$.

Evaluated crystallite size of Co₃O₄@NC was D₀₀₂ = ~ 52nm, for the highest intense peak corresponding to the plane (002) at 2$\theta$ =23.71^o.[17–19] The interlayer spacing determined by Bragg’s d= ${\lambda }/2\text{*}\text{s}\text{i}\text{n}\left( \theta \right)$ law with similar variables as debye-sherrer expression for the plane (002) d₀₀₂= 0.41 nm. Observed crystalline structure, crystalline size and interlayer spacing are in match with the previous reports.[19]

To affirm the formation and phase analysis of the synthesized carbon and the composite Co₃O₄@NC, Raman spectroscopic experiment has been carried out. As shown in the Fig. 1(b), D/G bands observed in both the cases for bare NC and the composite Co₃O₄@NC. The ratios of the intensities of D to G (= I_D/I_G) bands are observed to be 1.07 and 1.06 for NC and composite Co₃O₄@NC by which the presence of reduced graphene oxide (rGO). However, for the Co₃O₄@NC 422, 538, 636 and 784 corresponding to the E_g (R), F_1g (IN), 3F_2g (R), and 2F_2u (IN) respectively where, R, IN described as raman active and raman inactive modes respectively.[20, 21] With the observed XRD pattern and raman spectra analysis the affirmation of spinel Co3O4 with the raman active and inactive modes with “Fd3m” symmetry.[20]

EDS mapping & spectra

Affirmation of the present constituents in the composite of Co₃O₄@NC analyzed by the scanning transmission electron microscopy (STEM) based Elemental dispersion spectra (EDS). However, the elemental mapping of synthesized materials is an important information for the understanding of uniform distribution of elements which affects at the level application. Figure 2 (a, b, c) shows the elemental mapping of Co, C and O respectively. Figure 2 (d, e) displays combined EDS mapping image and observed EDS spectra defining the uniform distribution of the constituents and the atomic and mass percentages. Observed atomic (At%) and mass (Wt%) attached in Fig. 2 (e) and in Supplementary figure, SI.2 for Co₃O₄@NC.

X-ray Photoelectron Spectroscopy (XPS)

The XPS measurement was carried out for Co₃O₄@NC within the energy range of 0 to 900eV as displayed in Fig. 3(a), which affirms the presence of C, Co, and O. Figure 3(b) the XPS spectra of C1s shows the binding energies of C = C, C-O and O-C = O at the binding energies as 285.25 eV, 286.65 eV and 288.76 eV respectively in which carbon bonds corresponds to aromatic carbon.[21, 22] and the presence of O-C = O corresponds to the formation of reduced graphene oxide (rGO), generated by biomass that is neem leaf.[21, 23]. Mingguang Chen et.al also reported the formation of rGO with copper oxide (Cu₂O) resulting in nano-composite as rGO/Cu₂O in which the presence of O-C = O also observed.[23] However, the peaks for O1s observed as shown in the XPS spectra Fig. 3(c), at 533.21 eV and 535.15 eV which corresponds to the Co-O and O-H. Moreover, the spectra of Co2p displayed in Fig. 3(d), separated in two sections at the binding energies in which 780.89 eV, 796.26 eV belongs to Co 2p_1/2 and 782.41eV, 798.50 belongs to Co2p_3/2 respectively. Along with the XPS spectra, XRD and raman spectra are also in agreement to the formation rGO and the composite formation.

HRTEM

The high resolution transmission electron microscopy (HRTEM) analysis was carried out by dispersing 1 mg of the powdered sample in 5 µl was drop coated on a TEM grid, was dried under infrared (IR) lamp and analyzed using FEI, TECNAI G2 F20 instrument operated at an accelerated voltage of 200 kV (C_s = 0.6 mm, resolution 1.7A^o. The high resolution transmission electron microscopy (HRTEM) analysis was carried out for neem carbon. The HRTEM images displayed in Fig. 3, in which Fig. 4(a) shows the images of the resolution 20nm and other Fig. 4(b) are of resolution 5nm. However, for neem carbon, nanocrystal sizes ranges from 2.55nm to 4.46nm.[24]

Thermal Gravimetric Analysis (TGA) and BET Study:

The TGA graph shows the Fig. 5 weight (%) vs temperature (⁰C), heating rate of the sample is 10 ⁰C per minute up to 900 ⁰C. TGA profile shows that up to 500 ⁰C carbon is burning in the oxidative environment. The remaining residue was the actual metal alloy metal loading is shown in Fig. 5, commercial Ptc is 40wt%, Co₃O₄@NC 39% in this neem carbon already have the gradients naturally is prove the TGA. The Co₃O₄@NC shows the higher stability than commercial Ptc 40 wt% at higher temperatures.

Electrochemical characterization

A standard 3- electrode setup, consisting of a glassy carbon electrode (GCE) coated on with active catalyst as a working electrode (WE), a graphite rod as a counter electrode (CE)and an Hg/HgO (mercury oxide) as a reference electrode (RE), was used to perform all the single electrode electrochemical measurements. All the potential measurement ranges from 0 V to 1.1 V at various sweep rates. This equipment used for performing cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) has been carried out with the use of rotating disk electrode (RRDE) by VMP-3 model Biologic Potentiostat. The CV scanning rate is 50 mv/second and LSV scanning rate is 10 mv/second. The obtained current was normalized with the geometrical surface area of the working electrode. This GCE area is used for the calculating the current density. The voltage potentials were converted from Hg/HgO to V vs RHE with the use of following expression:[25, 26]

E_RHE= E_Hg/HgO + 0.0983+ (pH x 0.0592) (2)

Where, E_RHE is the converted potential from reference electrode to the reversible hydrogen electrode (RHE), 0.098V is the potential difference between Standard hydrogen electrode (SHE) and reference electrode Hg/HgO, E_Hg/HgO is the applied potential before the conversion between the working electrode and reference electrode Hg/HgO.

Electrode preparation:

All the electrodes were prepared with glassy carbon electrode (GCE) substrate of area 0.196cm².This GCE was cleaned with 0.05 and 0.3 µm alumina slurries. 10µl of the catalyst-Ptc 40 wt% slurry prepared by mixing 5 mg of the active catalyst, 5 microliter 0.05% nafion solution binder in the isopropyl alcohol (IPA): H₂O (1:3) solvent along with the sonication for 90 minutes. Coating of the catalyst carried out along with the drying of it under infrared lamp for 1 hour. Prepared electrode was used for the electrochemical measurements using standard 3 electrode system with 0.1M KOH solution.

Potentiostatic Voltammetric Analysis

The determination and analysis of the potentiostatic parameters were analyzed by carrying out standard experiments such as cyclic voltammetry (CV), linear sweep voltammetry (LSV). The observed short circuit current density (Jsc) and open circuit potentials highly recommend the application of Co₃O₄@NC as an ORR catalyst for the fuel cell with nearly close open circuit potential. The open circuit potential of the electrode is most important in the case of ORR as the reduction occurs above the region of the open circuit potential (OCP) considering the water splitting potential of 1.23V vs reversible hydrogen electrode (RHE), The potentials were converted from V vs Hg/HgO to V vs RHE. The CV plot and LSV plot has been shown in the SI.4 and Fig. 6 (a) respectively. The onset potential is an important parameter for the AEMFC, as the standard platinum based Ptc 40 wt% and Co₃O₄@NC shows nearly equal onset potential. With the use of Fig. 6 (a) onset potentials were determined for Ptc 40wt% and Co₃O₄@NC which are 1.13V vs RHE and 1.14 V vs RHE as displayed in Fig. 6 (b) which was evaluated by the point at which current density commences to zero. The onset potential is quite similar for both the cases which makes Co₃O₄@NC catalyst a cost-effective alternative to Ptc 40wt%. The higher onset potentials (Eon) promotes higher catalytic performance in the process of ORR for the choice of catalyst. Even though the onset potentials are close to each other, the current density was higher in the case of Ptc 40 wt% which makes it a high power catalyst as compared to the synthesized Co₃O₄@NC.

Moreover, the kinetics of the system under study analyzed by Tafel plots for both Ptc 40 wt% and Co₃O₄@NC. Figure 6 (c) displays the Tafel plot for the Ptc 40 wt% and Co₃O₄@NC with comparable tafel slopes. The Tafel plot was determined by the use of LSV curves. Tafel slope for Ptc 40 wt% and Co₃O₄@NC were 106 mV/dec and 120 mV/dec respectively as displayed in Fig. 6 (c). Synthesized catalyst Co₃O₄@NC shows ~ 13% higher slope as compared to standard commercial catalyst-Ptc 40 wt% which is quite low and can be used as a low cost alternative. The higher current density and catalytic activity observed for Co₃O₄@NC was due to the composite of Co₃O₄ with porous carbon which decreases the charge transfer resistance.[3, 21].

Impedance spectroscopy of the standard Ptc 40% and Co₃O₄@NC

Electrochemical Impedance Spectroscopy (EIS) has been carried out for the analysis of series resistance by the analysis of nyquist plot. The EIS has been carried out using the standard three electrode electrochemical system for both Ptc 40 wt% and Co₃O₄@NC. The impedance analysis explains about the kinetics of the system under study. The Fig. 6 (d) shows the impedance characteristics of electrodes under study which are Ptc 40 wt% and Co₃O₄@NC. With the use of the nyquist plot ohmic resistance (Rs) and charge transfer resistance (Rct) evaluated as shown in the Table 1.[25] The Rs for the platinum is 0.5 times of Co₃O₄@NC but the Rct is 2.8 times less for Co₃O₄@NC comparing to the commercial platinum electrode which promotes the merits of Co₃O₄@NC over the platinum electrodes high frequency performance. It also enabled the use of Co₃O₄@NC catalyst for the high frequency application.

Table 1

Electrochemical properties for Ptc 40 wt% and Co₃O₄@NC such as ohmic resistance (Rs), charge transfer resistance (Rct) and onset potential (Eon).
Sample	Rs (ohm)	Rct (ohm)	Eon (V vs RHE)
Ptc 40 wt%	41.09	7.5	1.13
Co₃O₄@NC	83.42	2.65	1.14

Fuel Cell Testing:

The membrane electrolyte assembly (MEA) fabrication method used to prepare AEMFC. Kepton tape, FuMA Tech-FAA membrane were for sub gasket and as the anion exchange electrolyte membrane respectively. The schematic representation of AEMFC assembly has been displayed in Scheme 2.[27]

The MEA was prepared of the area 2 x 2 = 4 cm² area with standard fixture. Standard commercial platinum based catalyst Ptc 40 wt% used as the anode MEA. However, the synthesized Co₃O₄@NC was used as cathode with multiple loadings considering the area under application which was prepared by MEA fabrication method. The optimization of cathode loading has been done by varying the cathode loading as 1mg/cm², 2mg/cm² and 3 mg/cm² along with the anode, which was kept to be 1mg/cm².

The schematic of the working of AEMFC, displayed in Fig. 7 (a). In the case of AEMFC with purging of the fuel as hydrogen (H₂) and oxygen (O₂)/Air oxidant, the half-cell reactions and the overall reactions are:[27]

Half- ell reactions:

H₂ + 2OH⁻ → 2H₂O + 2e⁻ ; E_anode = 0.83 V vs SHE (3)

0.5 O₂ + H₂O + 2e⁻ → 2OH⁻ ; E_cathode = 0.40 V vs SHE (4)

Overall:

H₂ + 0.5 O₂ → H₂O; E_cel = 1.23 V vs SHE (5)

In the process of the oxygen reduction, hydroxide ions are generated at cathode which travels to the anode through anion conducting polymer electrolyte, at which hydroxide ions combines with hydrogen resulting in the formation of water. Moreover, the electrons generated during the oxidation of H₂, moves by circuit connected to the cathode at which it participates in the process of reducing oxygen to generate OH⁻.

Figure 7 (b) shows the comparative I-V polarization plots generated by the single cell (4 cm²) Ptc 40 wt% with distinct mass loadings of catalyst. The initial measurements were carried out with the mass loading of 1mg/cm² for both anode and cathode resulting in highest power density as shown in the Table 2. The AEMFC system with Ptc 40 wt% as cathode and anode with the mass loading of 1 1mg/cm² was taken as benchmark for further experiments.

Table 2

MEA performance and loading details.
MEA No.	Catalyst loading (mg/cm² )		Material		OCV	Power Density @0.6V
	Anode	Cathode	Anode	Cathode
1	1	1	Pt/c	Pt/c	0.957	61.5
2	1	1	Pt/c	Co₃O₄@NC	0.925	42.6
3	1	2	Pt/c	Co₃O₄@NC	0.82	8.5
4	1	3	Pt/c	Co₃O₄@NC	0.81	7.6

Ptc 40 wt% based AEMFC supplied the open circuit voltage (OCV) of 0.957 V with the maximum power density 61.5 mw/cm² at 0.6 V. The observed parameters for the standard platinum and the prospective cathode catalyst -Co₃O₄@NC displayed in Table 2. Ptc 40 wt% as an anode and Co₃O₄@NC as cathode with 1 mg/cm² OCV was 0.925 V with maximum power density 42.60 mw/cm² at 0.6V. Observed results for the multiple combinations listed in the Table 2. 1mg/cm2 mass loading of Co₃O₄@NC showed highest power density comparing the other combinations with distinct massloading.

We illustrated the cost-effective synthesis of carbon from neem carbon (Biomass) and its combination with Co₃O₄has been achieved by scalable technique. The oxidation states and formation of Co₃O₄ has been affirmed by X-ray photoelectron microscopy and the bonds with the preset Carbon derived by Neem leaves. The structural, thermo-gravimetric and electrochemical properties along with the real world application of the catalyst Co₃O₄@NC for the oxygen reduction reaction (ORR) application has been demonstrated and characterized by the proven experimental techniques. Determination of the compatible and efficient ORR catalyst has been carried out by the performance analysis of the state of the art Ptc 40 wt% and the synthesized Co₃O₄@NC. The observed open circuit potential (OCP) of the Ptc 40 wt% and Co₃O₄@NC was 0.957V and 0.925V which is only 3.34% less than standard Ptc 40% for anion-exchange membrane fuel cell (AEMFC) with single-cell assembly. We believe, the application of the Co₃O₄@NC as a cost-effective and efficient ORR catalyst demonstration along with the combination of biomass based carbon will increase the research in the field of development of cost-effective catalyst development with minimal use of fossil fuels.

Supplementary information

XRD of KOH activated neem carbon, EDS of Co₃O₄@NC, STEM image of CV Co₃O₄@NC for Co₃O₄@NC and Ptc 40 wt%., BET graphs for Co₃O₄@NC, neem carbon and Ptc 40 wt%.

Acknowledgement: D.N. gratefully acknowledge Chhatrapati Shahu Maharaj Research, Training and Human Development Institute (SARATHI) fellowship. S.S.G. acknowledges Department of Science and Technology (DST), India for PhD fellowship Scheme. A.P. acknowledges the Regional Test Centre (RTC) for the use of facilities at the Savitribai Phule Pune University.

Notes: The authors declare no competing financial interest

Ethical Approval: Not Applicable

Availability of Data and Materials: Available upon request.

Funding: The present study was carried out without financial support.

Author Contribution: DN: Conceptualization, Writing-Original Manuscript, Data Curation DSN: Formal Analysis, Writing-Original Manuscript, Methodology, SSG: Conceptualization, GYS: Validation, SLP: Resouces, VJ: Writing - Review & Editing, Project administration AP: Writing - Review & Editing, Supervision, and all authors have read and approved the manuscript.

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Schemes 1 and 2 are available in the Supplementary Files section.

No competing interests reported.

supplementaryinformation.docx
Scheme1.png
Scheme 1. Schematic diagram for the synthesis of functional carbon from dead Neem (NC) leaves and the final product as composite of Co₃O₄@NC.
Scheme2.png
Scheme 2 Schematic represenation of fabrication process of the single anion-exchange membrane fuel cell by using the catalysts-Co₃O₄@NC as cathode material.

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Low Cost Co₃O₄ & Neem Leaves Derived Carbon Composite: High-Performance Oxygen Reduction Electro-catalyst for AEMFC

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