Arrayed Cobalt Phosphide Electrocatalyst Achieves Low Energy Consumption and Persistent H2 Liberation from Anodic Chemical Conversion
Kai Zhang, Gong Zhang, Qinghua Ji, Jiuhui Qu, Huijuan Liu
Abstract
Abstract 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.