Electronic modulation of cobalt phosphide nanosheet arrays via copper doping for highly efficient neutral-pH overall water splitting

We report here, an effective strategy to optimize the electronic structure of CoP using copper doping, for greatly enhancing the intrinsic activity and conductivity of CoP in neutral-pH water splitting. As a result, the as-synthesized 3D self-supported Cu-doped CoP nanosheet arrays on carbon paper (Cu-CoP NAs/CP) exhibits admirable electrocatalytic performance toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with overpotentials of 81 and 411 mV at 10 mA cm−2 in 1.0 M PBS (Phosphate Buffer Solution), respectively. Moreover, a neutral electrolyzer, using Cu-CoP NAs/CP as both the anode and cathode, achieves a low cell voltage of 1.72 V at 10 mA cm−2, superior to that of the typical Pt/C||IrO2 couple (1.81 V) and of most of the state-of-the-art bifunctional electrocatalysts. Impressively, the electrolyzer can be driven by a single AA battery (∼1.5 V), indicating its practicality in neutral water or seawater splitting. Experimental and density functional theory (DFT) calculations results reveal that the incorporation of Cu into CoP can effectively improve the conductivity and optimize the electronic structure to facilitate the H* adsorption and desorption and the formation of O* intermediates (generated CoOOH active species), thus yielding superior HER and OER catalytic activities. This study opens up a promising way to rationally design highly efficient and low-cost electrocatalysts for electrocatalysis applications.