Efficient light absorption and high energy of charge carriers of zinc cadmium sulfide (ZCS) make this semiconductor attractive for many photocatalytic reactions. Despite marked successes in shape-controlled synthesis of ZCS central to their photocatalytic performance, recombination of charge carriers as they migrate through the nanoscale particles result in losses of excitation energy markedly reducing photocatalytic activity of ZCS and other heterogeneous photocatalysts. Here we show that electrostatic asymmetry of single-crystalline ZCS with planar geometry assists charge separation and substantially increase the yield of photocatalytic reactions. The synthesized ZCS nanorods and nanoplates with identical chemical composition were found to have markedly different photocatalytic activity for evolution of hydrogen in water. Despite much smaller specific surface areas, the ~ 500 nm wide nanoplates displayed hydrogen evolution rate 12 times higher than the ~ 35 nm long nanorods also outperforming other ZCS photocatalysts. Experimental and computational data indicate that the homo and heterojunction-free ZCS nanoplates with continuous wurtzite lattice behave essentially as nanoscale dipoles. Electric-field-directed migration of charge carriers stimulates their localization on opposite parts of the nanoplates. Direct imaging of intraparticle electrical field using off-axis electron holography confirmed their electrostatic asymmetry. Polarization-enhanced charge separation provides a new pathway to efficient and stable photocatalysts for sustainable energy technologies.