Co/CoP Heterojunction on Hierarchically Ordered Porous Carbon as a Highly Efficient Electrocatalyst for Hydrogen and Oxygen Evolution

Designing non-precious electrocatalysts to synergistically achieve a facilitated mass/electron transfer and exposure of abundant active sites is highly desired but remains a significant challenge. Herein, a composite electrocatalyst consisting of highly dispersed Co/CoP heterojunction embedded within a hierarchically ordered macroporous-mesoporous-microporous carbon matrix (Co/CoP@HOMC) is rationally designed through the pyrolysis of polystyrene sphere-templated zeolite imidazolate framework-67 (ZIF-67) assemblies. The combined experimental and theoretical calculations reveal that Co/CoP interfaces not only provide richly exposed active sites but also optimize hydrogen/water absorption free energy via electronic coupling, while the interconnected macroporous structure enables a superior mass transfer to all accessible active sites. As a result, the as-developed Co/CoP@HOMC composites exhibit outstanding catalytic activity with overpotentials of only 120 and 260 mV at 10 mA cm(-2) for the hydrogen evolution reaction and oxygen evolution reaction in 1.0 m KOH, respectively. Moreover, an alkaline electrolyzer constructed by Co/CoP@HOMC requires an ultralow cell voltage of 1.54 V to achieve 10 mA cm(-2), outperforming that of the Pt@C||IrO2@C couple (1.64 V).