An ultra-high mass-loading transition metal phosphide electrocatalyst for efficient water splitting and ultra-durable zinc-air batteries

The development of sustainable energy conversion and storage technologies is an effective approach to relieve the increasingly severe global energy crisis. Herein, a facile reductive electrosynthesis approach, using Pluronic P123 as a structure-directing agent, is reported to prepare an electrically conductive, electrochemically stable, and porous Ni-Co-Mn phosphide (NCMP) electrocatalyst with a super-high mass loading of 22.6 mg cm-2, feasible for industrial-level applications. The NCMP electrocatalyst exhibits superior trifunctional electrocatalytic activities toward the hydrogen evolution reaction (eta j=10 = 100 mV), oxygen evolution reaction (eta j=50 = 218 mV), and oxygen reduction reaction (half-wave potential = 0.74 V vs. reversible hydrogen electrode) in alkaline electrolytes. The NCMP-based cell delivers an overall water-splitting voltage of 1.53 V at a rate of 10 mA cm-2, which is lower than that of the benchmark Pt/C(-)-RuO2/C(+) system. The NCMP-based zinc-air battery exhibits a high power density of 148 mW cm-2, a high specific energy of similar to 932 W h kgZn-1, and excellent cycling stability of over 6000 cycles at 5 mA cm-2. Mechanistic studies through theoretical calculations revealed that a trimetallic species formed by Ni, Co, and Mn is the most catalytically active site. It is anticipated that this novel reductive electrosynthesis approach may extend to other electrodeposition processes and pave the way to better meet the existing and expected energy demands. We demonstrate the practical applicability of Ni-Co-Mn-P as an efficient electrocatalyst active in all the HER, OER, and ORR processes even under an ultra-high mass loading of over 22 mg cm-2.