Arrayed Cobalt Phosphide Electrocatalyst Achieves Low Energy Consumption and Persistent H(2) Liberation from Anodic Chemical Conversion

Electrochemical reduction of water to hydrogen (H(2)) offers a promising strategy for production of clean energy, but the design and optimization of electrochemical apparatus present challenges in terms of H(2) recovery and energy consumption. Using cobalt phosphide nanoarrays (Co(2)P/CoP NAs) as a charge mediator, we effectively separated the H(2) and O(2) evolution of alkaline water electrolysis in time, thereby achieving a membrane-free pathway for H(2) purification. The hierarchical array structure and synergistic optimization of the electronic configuration of metallic Co(2)P and metalloid CoP make the Co(2)P/CoP NAs high-efficiency bifunctional electrocatalysts for both charge storage and hydrogen evolution. Theoretical investigations revealed that the introduction of Co(2)P into CoP leads to a moderate hydrogen adsorption free energy and low water dissociation barrier, which are beneficial for boosting HER activity. Meanwhile, Co(2)P/CoP NAs with high capacitance could maintain a cathodic H(2) evolution time of 1500 s at 10 mA cm(−2) 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. [Image: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40820-020-00486-2) contains supplementary material, which is available to authorized users.