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 long-term 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.