Phase‐Junction Electrocatalysts towards Enhanced Hydrogen Evolution Reaction in Alkaline Media

To ensure sustainable hydrogen production by water electrolysis, robust, earth‐abundant, and high‐efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase‐junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c‐NiP2/m‐NiP2) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm−2) for NiP2‐650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c‐NiP2 and m‐NiP2, respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons. Constructing phase‐junction electrocatalysts could effectively accelerate the Volmer step and modulate the electronic structure at the interface. NiP2‐650(c/m) shows an overpotential η10 of 134 mV vs. RHE at 10 mA cm−2 and a Tafel slope of 67 mV dec−1, which is significantly reduced by 26 % and 96 % compared with c‐NiP2 and m‐NiP2, respectively.