Amorphous Multi-elements Electrocatalysts with Tunable Bifunctionality toward Overall Water Splitting

Economically producing hydrogen via electrocatalytic water splitting requires highly efficient and low-cost catalysts and scalable synthetic strategies. Herein, we present the preparation of hierarchically structured multi-elements water splitting electrocatalysts consisting of Fe, Co, Ni, S, P, and O with a one-step electrodeposition method. By tuning of the non-metal compositions of the catalysts, the electrochemical performances of the catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1 M KOH can be rationally modified, respectively. Under the optimum conditions, current densities of 100 and 1000 mA cm(-2) were obtained at overpotentials of only 135 and 264 mV on the HER catalyst and 258 and 360 mV on the OER catalyst, respectively. When the best-performing HER and OER catalysts were assembled in a two-electrode system for overall water splitting, a current density of 10 mA cm(-2) could be obtained under a cell voltage of 1.46 V with longterm durability. As far as we know, this is among the lowest voltages ever reported for a two-electrode electrolyzer based upon earth-abundant, elements. Moreover, the catalysts can be facilely assembled on commercially available Ni mesh and demonstrate even higher performance, indicating their great potential for scaled-up water electrolysis. We further demonstrate that S and P play different and pivotal roles in modifying the apparent and intrinsic electrocatalytic activity of the as-prepared amorphous electrocatalysts, therefore pointing out a pathway toward the optimization of multi-elements catalysts.