Revised Oxygen Evolution Reaction Activity Trends for First-Row Transition-Metal (Oxy)hydroxides in Alkaline Media

Abstract

First-row transition-metal oxides and (oxy)hydroxides catalyze the oxygen evolution reaction (OER) in alkaline media. Understanding the intrinsic catalytic activity provides insight into improved catalyst design. Experimental and computationally predicted activity trends, however, have varied substantially. Here we describe a new OER activity trend for nominally oxyhydroxide thin films of Ni(Fe)O(x)H(y) > Co(Fe)O(x)H(y) > FeO(x)H(y)-AuO(x) > FeO(x)H(y) > CoO(x)H(y) > NiO(x)H(y) > MnO(x)H(y). This intrinsic trend has been previously obscured by electrolyte impurities, potential-dependent electrical conductivity, and difficulty in correcting for surface-area or mass-loading differences. A quartz-crystal microbalance was used to monitor mass in situ and X-ray photoelectron spectroscopy to measure composition and impurity levels. These new results provide a basis for comparison to theory and help guide the design of improved catalyst systems.

Environmental TEM Investigation of Electrochemical Stability of Perovskite and Ruddlesden–Popper Type Manganite Oxygen Evolution Catalysts

“…[1][2][3][4][5][6][7] Next to scarce noble metal oxides, several first-row transition metal oxides and, in particular, perovskite-based systems with the general formula ABO 3 perform well as OER catalysts. [6][7][8][9][10] Theoretical studies suggest that the catalytic activity of the four-electron transfer reaction forming molecular O 2 depends on strength and flexibility of the metal-oxygen bond, which can shift the redox activity from metal to lattice oxygen surface sites due to ligand hole formation. [7,28,34,39,40] Thus, an understanding of the underlying microscopic mechanisms, the nature of active sites, and catalyst stability is necessary to rationalize the search for active and stable catalysts.…”

Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films

“…The behavior of Fe-doped Ni (Fe:Ni) oxide films under basic conditions (1 M KOH) has been revisited (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) and in this recent body of work, the role of Fe in these films has come under debate. X-ray absorption spectra of Fe:Ni oxide films supported by computational studies have led to the contention that Fe 3+ species are the active sites for water oxidation (13).…”

“…X-ray absorption spectra of Fe:Ni oxide films supported by computational studies have led to the contention that Fe 3+ species are the active sites for water oxidation (13). The conductivity of the metal (Ni and Co) oxido framework has been observed to increase with Fe content, with the oxide also potentially serving as a scaffold for Fe active sites (16,17). Interestingly, unary Fe oxide films, however, are inferior OER catalysts.…”

“…Interestingly, unary Fe oxide films, however, are inferior OER catalysts. Whereas iron oxide displays modest intrinsic activity at high overpotentials (η > 350 mV) (17), at low overpotentials (η < 300 mV) the activity of the films is poor (17,18,(20)(21)(22), even as ultrathin submonolayer films (22). Interestingly, the Tafel slope of Fe:Ni oxido films changes with increasing Fe content (7).…”

Operando Analyses of Solar Fuels Light Absorbers and Catalysts

“…Theoretical modelling and experiments by Diaz-Morales et al [39], and results from a variant of scanning electrochemical microscopy designed by Ahn and Bard [53], furthermore support the assignment of Fe as the active site. Furthermore, it has been proposed that even the poor OER activity of pure FeOOH does not match with a revised general trend for transition metal oxyhydroxides [54], and that a high intrinsic activity of Fe sites could be masked by the lack of electronic conductivity in…”