Engineering Electronic Structures of Nickel Cobalt Phosphide via Iron Doping for Efficient Overall Water Splitting

Abstract

Efficient and low‐cost bifunctional OER/HER electrocatalysts are important for overall water splitting. Herein, three‐dimensional self‐supported Fe‐doped NiCo‐based phosphide nanosheets arrays are in‐situ grown on carbon fiber paper. The catalyst shows superior bifunctional activity, with an OER overpotential of 230 mV and an HER overpotential of 95 mV at 10 mA cm−2 in alkaline electrolyte. It is evidenced that the Fe doping facilitates electron transfer from Co/Ni to P, thus optimizing the electronic structures of both Ni and Co active sites, in turn greatly enhancing intrinsic OER and HER activities. The OER and HER turnover frequency are largely improved after Fe doping. When used as both anode and cathode for water splitting, the catalyst enables the electrolyzer to achieve 10 mV cm−2 at a low cell voltage of 1.59 V with a long‐term stability up to 35 h. This work highlights the synergy effect of multi‐metal‐based phosphides for efficient water electrocatalysis.

Recent Progresses in Engineering of Ni and Co based Phosphides for Effective Electrocatalytic Water Splitting

“…The phosphorous‐phosphorous bonding presence in TMPs was usually less stable which makes the OER/HER process in a facile manner. By way of introducing, the tremendously active Co and Ni based phosphides, have been studied for total water splitting which showed considerable activity and stability [58–61] . The recent report with the electronic modulation of multi shelled CoP hollow spheres shows significant improvement in the HER [102] .…”

“…The doping results, the strong chemical structural changes in the system results synergistic improvement in the electrocatalytic performance of the catalyst. In that line, the Fe doping in the NiCo system drastically improves the intrinsic activity of the catalyst in both OER as well as HER process in alkaline water electrolysis [61] . Pang et al .…”

“…In HER, the presence of phosphide with the presence of P from pnictogenides family with sufficient electronegativity can bring H + from the acidic electrolyte effectively. During HER and OER mechanistic steps, the presence of metal phosphides showed enhanced charge transfer with high electrical conductivity of phosphides compared to their own oxide counterparts [16,55–61] . Hence, it is highly desired to visualize the importance of Ni and Co based phosphides towards electrocatalytic water splitting with such high improvements towards AWS [1,62–65] .…”

“…In general, increasing metal sites simultaneously increases the electrocatalytic efficiency in the OER/HER studies in both alkaline and acidic conditions [129] . In recent times, the concept of bimetal TMPs was studied as a better catalyst for alkaline water electrolysis [61] . The doping results, the strong chemical structural changes in the system results synergistic improvement in the electrocatalytic performance of the catalyst.…”

“…Pang et al . studied the reason behind the increased activity with such Fe‐doping in the TMPs [61] . The strong electronic interaction of Fe results in the increasing electron transfer from Ni/Co to P which endorses the OER/HER efficiency with Ni/Co metal in the water splitting.…”