Template-stabilized oxidic nickel oxygen evolution catalysts

Abstract

<jats:p>Earth-abundant oxygen evolution catalysts (OECs) with extended stability in acid can be constructed by embedding active sites within an acid-stable metal-oxide framework. Here, we report stable NiPbO<jats:sub>x</jats:sub> films that are able to perform oxygen evolution reaction (OER) catalysis for extended periods of operation (&gt;20 h) in acidic solutions of pH 2.5; conversely, native NiO<jats:sub>x</jats:sub> catalyst films dissolve immediately. In situ X-ray absorption spectroscopy and ex situ X-ray photoelectron spectroscopy reveal that PbO<jats:sub>2</jats:sub> is unperturbed after addition of Ni and/or Fe into the lattice, which serves as an acid-stable, conductive framework for embedded OER active centers. The ability to perform OER in acid allows the mechanism of Fe doping on Ni catalysts to be further probed. Catalyst activity with Fe doping of oxidic Ni OEC under acid conditions, as compared to neutral or basic conditions, supports the contention that role of Fe<jats:sup>3+</jats:sup> in enhancing catalytic activity in Ni oxide catalysts arises from its Lewis acid properties.</jats:p>

Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment

“…For this purpose, numerous research groups have been working on the development of transition metal oxides for OER in acid. [ 192–204 ] Mn‐based oxides and Co‐based oxides are the two most widely investigated transition metal oxides. First, Mn‐based oxides are considered for OER in acid due to the nature of self‐healing to compensate their dissolution in acid.…”

“…First, Mn‐based oxides are considered for OER in acid due to the nature of self‐healing to compensate their dissolution in acid. [ 192 ] Up to now, numerous Mn‐based oxides have been fabricated and optimized, such as TiO 2 ‐incorporated MnO 2 , [ 138 ] hausmannite‐like intermediate (α‐Mn 3 O 4 ), [ 193 ] MnO 2 with metastable Mn 3+ , [ 194 ] Co/Mo‐doped MnO 2 (MnMoCoO), [ 195 ] Cu 1.5 Mn 1.5 O 4 :10F, [ 196 ] Ni x Mn 1− x Sb 1.6–1.8 O y , [ 197 ] (Mn 0.9 Nb 0.1 )O 2 :10F, [ 198 ] NiPbO x , [ 199 ] etc. Among these Mn‐based oxides, the well‐designed gamma manganese oxides (γ‐MnO 2 ) showed a long‐term stability of 8000 h between 1.6 and 1.75 V versus RHE (at 10 mA cm −2 ) in a pH = 2 electrolyte.…”

Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction

“…Iron doping of metal oxide films has long been known to increase overall OER activity of metal oxide OER catalysts 42,43 . The behaviour of Fe in Ni-OECs has been revisited 44 , and the role of Fe has been ascribed to various factors, including active site Fe 4 + or higher valent species [45][46][47] , near neighbour Fe effects on Ni resulting from strain on the oxide lattice [48][49][50][51] , active oxygen intermediates at Ni-Fe sites [52][53][54] , Fe induced partial-chargetransfer to Ni sites 55,56 , and Fe acting as a Lewis acid that promotes charge transfer character and favourable energetics for Ni oxyl formation 57,58 . Quizzically, though detected by Mössbauer spectroscopy, the presence of Fe 4+ does not correlate with the observed catalytic activity 59 .…”

Electrocatalytic acidic oxygen evolution reaction: From nanocrystals to single atoms

“…tested the in situ XAS of stable NiPbO x films (Figure 11D), combined ex situ X‐ray photoelectron spectroscopy (Figure 11C) found that PbO 2 is unperturbed after addition of Ni and/or Fe into the lattice, which serves as an acid‐stable, conductive framework for embedded OER active centers. [ 159 ]…”

“…Reproduced with permission: Copyright 2020, PNAS. [ 159 ] (E,F) In situ XANES spectra of Li‐IrO x and IrO 2 ‐L. (G,H) In situ EXAFS spectra of Li‐IrO x and IrO 2 ‐L.…”