A nickel iron diselenide-derived efficient oxygen-evolution catalyst

Abstract

Efficient oxygen-evolution reaction catalysts are required for the cost-effective generation of solar fuels. Metal selenides have been reported as promising oxygen-evolution catalysts; however, their active forms are yet to be elucidated. Here we show that a representative selenide catalyst, nickel selenide, is entirely converted into nickel hydroxide under oxygen-evolution conditions. This result indicates that metal selenides are unstable during oxygen evolution, and the in situ generated metal oxides are responsible for their activity. This knowledge inspired us to synthesize nanostructured nickel iron diselenide, a hitherto unknown metal selenide, and to use it as a templating precursor to a highly active nickel iron oxide catalyst. This selenide-derived oxide catalyses oxygen evolution with an overpotential of only 195 mV for 10 mA cm−2. Our work underscores the importance of identifying the active species of oxygen-evolution catalysts, and demonstrates how such knowledge can be applied to develop better catalysts.

Liquid Exfoliated Co(OH)2 Nanosheets as Low‐Cost, Yet High‐Performance, Catalysts for the Oxygen Evolution Reaction

“…Similar to hydrogen evolution electrocatalysis, [46,47] nanosheet edges are often assumed to be active for OER catalysis. [5][6][7] While Chen and Selloni [48] used DFT to suggest edges to be the most likely active sites for Co(OH)2, this has not been confirmed experimentally. In addition, Song et al [6] linked the improved activity of their exfoliated LDHs compared to bulk samples to the increased number of edge sites but highlighted the requirement for a rigorous study to prove this correlation.…”

“…[28,30,31] However, in the past, LDH nanosheets have been produced by relatively complex methods such as hydrothermal synthesis coupled with exfoliation by ion exchange. [6,7,24,32] Here we take a simpler approach, using LPE as a top-down method to produce Co(OH)2 nanosheets directly from the parent layered crystal. Liquid phase exfoliation is a simple, robust technique which can produce large volumes (>100s of litres) [25] of nanosheet dispersions in ambient conditions.…”

“…This approach has led to the demonstration of some impressive materials. [7,9,[12][13][14] However, it also has significant weakness in that many of the high-performance materials which have been demonstrated are complex structures [7,9,12,13] (e.g. gelled FeCoW oxyhydroxide [9] or highly porous NixFe1-xSe2 nanoplates [7] ) which may be challenging to produce cheaply in large quantities.…”

“…Using an optimised electrode thickness of 70 m and tuning the electrolyte concentration and temperature, we were able to achieve current densities of 50 mA cm -2 at overpotentials as low as 235 mV, only 25 mV above the state-of-the-art (50 mA cm -2 @ 210 mV). [7] …”

“…[4,5] For alkaline electrolysis, oxides/hydroxides or chalcogenides of Ni, Co and/or Fe have proven to be the most effective catalysts. [6][7][8][9][10] Of these, 2-dimensional materials such as layered double hydroxides (LDH), [5,6,11] have attracted much focus, achieving current densities of 50 mA cm -2 at overpotentials as low as ~210 mV. [7] However, the best performing materials tend to require complex synthesis such that a system which combines highperformance with low cost has yet to be demonstrated.…”