Experimental and Computational Evidence of Highly Active Fe Impurity Sites on the Surface of Oxidized Au for the Electrocatalytic Oxidation of Water in Basic Media

Abstract

Addition of Fe to Ni-and Co-based (oxy)hydroxides significantly enhances the activity of these materials for electrochemical oxygen evolution reaction (OER). Here, we show that Fe cations bound to the surface of oxidized Au enhance its OER activity, the OER activity increasing with increasing surface concentration of Fe. Density functional theory analysis of the energetics of the OER revealed that oxygen evolution over Fe cations bound to a hydroxylterminated oxidized Au surface (Fe-Au2O3) occurs at an overpotential 0.43 V lower than that at which the OER occurs on hydroxylated Au2O3 (0.86 V). This finding agrees very well with experimental observation and is a consequence of the more optimal binding energetics for the OER reaction intermediates at Fe cations bound to the surface of Au2O3. These findings suggest that the enhanced OER activity reported recently upon low-potential cycling of Au may be due to surface Fe impurities rather than to "superactive" Au(III) surfaquo species.3

Ambient-Pressure XPS Study of a Ni–Fe Electrocatalyst for the Oxygen Evolution Reaction

“…We note that the observed spectral change is within a potential region where Au electrodes undergo surface oxide formation. 27,28 However, if Au oxidation took place, we would expect the Au 4f spectra to exhibit a new component at ~1 eV higher binding energy; such a spectral change was not detected in our measurements ( Figure S7). The additional oxide species appears at a potential at which, according to the cyclic voltammogram, we do not yet expect oxidation of Ni(OH) 2 to NiOOH.…”

NiFe‐Based (Oxy)hydroxide Catalysts for Oxygen Evolution Reaction in Non‐Acidic Electrolytes

“…However, it is generally accepted that the OER overpotential decreases dramatically for increase in Fe content from 0 to 10%, reaches a minimum at some concentrations in the range between 10% and 50% and further increases for Fe content higher than 50% (Figure 5b). Interestingly, despite the presence of Fe has a beneficial positive impact on the OER activity, [45,84,92] pure Fe oxyhydroxide electrodes were reported to catalyze the OER with high overpotentials in alkaline conditions. Ni hydroxides have been extensively studied as catalysts for OER and many Ni hydroxide based catalysts have been reported to exhibit superior OER activity in alkaline and near neutral borate buffered electrolyte.…”

Enhanced Electrocatalytic Oxygen Evolution in Au–Fe Nanoalloys

“…[2] In particular, mixedmetal or alloy electrodes are attracting great interest as viable alternatives to the expensive Ru and Ir-based catalysts. [8][9][10][11][12][13][14][15] This fact was not clearly realized before,b ecause the observation of as ignificant improvement of OER activity was hampered by the poor conductivity of the OER-active material containing the Fe 3+ species,typically FeOOH. [6,7] Va rious research groups demonstrated that Fe 3+ plays ak ey role in OER.…”

“…[8][9][10][11][12][13][14][15] This fact was not clearly realized before,b ecause the observation of as ignificant improvement of OER activity was hampered by the poor conductivity of the OER-active material containing the Fe 3+ species,typically FeOOH. [14,15] However,t hese electrodes are formed upon alkaline oxidation of Au surfaces and subsequent adsorption of Fe 3+ OER active sites,w hich does not allow ap recise control of iron-loading and overall chemical composition. [11][12][13][14][15] Tw o recent papers reported as ignificant improvement of OER activity in alkaline conditions when the surface of gold was doped with Fe 3+ species.…”

“…[6,7] Va rious research groups demonstrated that Fe 3+ plays ak ey role in OER. [11][12][13][14][15] Tw o recent papers reported as ignificant improvement of OER activity in alkaline conditions when the surface of gold was doped with Fe 3+ species. [14] On the other hand, lower values of overpotential and remarkable catalytic efficiencyw ere observed in the case of Fe 3+ species combined with more conductive host materials,like CoOOH or NiOOH.…”