Arrayed Cobalt Phosphide Electrocatalyst Achieves Low Energy Consumption and Persistent H Liberation from Anodic Chemical Conversion.

Electrochemical reduction of water to hydrogen (H) offers a promising strategy for production of clean energy, but the design and optimization of electrochemical apparatus present challenges in terms of H recovery and energy consumption. Using cobalt phosphide nanoarrays (CoP/CoP NAs) as a charge mediator, we effectively separated the H and O evolution of alkaline water electrolysis in time, thereby achieving a membrane-free pathway for H purification. The hierarchical array structure and synergistic optimization of the electronic configuration of metallic CoP and metalloid CoP make the CoP/CoP NAs high-efficiency bifunctional electrocatalysts for both charge storage and hydrogen evolution. Theoretical investigations revealed that the introduction of CoP into CoP leads to a moderate hydrogen adsorption free energy and low water dissociation barrier, which are beneficial for boosting HER activity. Meanwhile, CoP/CoP NAs with high capacitance could maintain a cathodic H evolution time of 1500 s at 10 mA cm driven by a low average voltage of 1.38 V. Alternatively, the energy stored in the mediator could be exhausted via coupling with the anodic oxidation of ammonia, whereby only 0.21 V was required to hold the current for 1188 s. This membrane-free architecture demonstrates the potential for developing hydrogen purification technology at low cost.