Identification of highly active Fe sites in (Ni,Fe)OOH for electrocatalytic water splitting.

Highly active catalysts for the oxygen evolution reaction (OER) are required for the development of photoelectrochemical devices that generate hydrogen efficiently from water using solar energy. Here, we identify the origin of a 500-fold OER activity enhancement that can be achieved with mixed (Ni,Fe)oxyhydroxides (Ni(1-x)Fe(x)OOH) over their pure Ni and Fe parent compounds, resulting in one of the most active currently known OER catalysts in alkaline electrolyte. Operando X-ray absorption spectroscopy (XAS) using high energy resolution fluorescence detection (HERFD) reveals that Fe(3+) in Ni(1-x)Fe(x)OOH occupies octahedral sites with unusually short Fe-O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra.

On the chemical state of Co oxide electrocatalysts during alkaline water splitting.

Resonant inelastic X-ray scattering and high-resolution X-ray absorption spectroscopy were used to identify the chemical state of a Co electrocatalyst in situ during the oxygen evolution reaction. After anodic electrodeposition onto Au(111) from a Co(2+)-containing electrolyte, the chemical environment of Co can be identified to be almost identical to CoOOH. With increasing potentials, a subtle increase of the Co oxidation state is observed, indicating a non-stoichiometric composition of the working OER catalyst containing a small fraction of Co(4+) sites.

An investigation of thin-film Ni-Fe oxide catalysts for the electrochemical evolution of oxygen.

A detailed investigation has been carried out of the structure and electrochemical activity of electrodeposited Ni-Fe films for the oxygen evolution reaction (OER) in alkaline electrolytes. Ni-Fe films with a bulk and surface composition of 40% Fe exhibit OER activities that are roughly 2 orders of magnitude higher than that of a freshly deposited Ni film and about 3 orders of magnitude higher than that of an Fe film. The freshly deposited Ni film increases in activity by as much as 20-fold during exposure to the electrolyte (KOH); however, all films containing Fe are stable as deposited.

Nanoscale electrodes by conducting atomic force microscopy: oxygen reduction kinetics at the Ptmid R:CsHSO4 interface.

We quantitatively characterized oxygen reduction kinetics at the nanoscale Ptmid R:CsHSO(4) interface at approximately 150 degrees C in humidified air using conducting atomic force microscopy (AFM) in conjunction with AC impedance spectroscopy and cyclic voltammetry. From the impedance measurements, oxygen reduction at Ptmid R:CsHSO(4) was found to comprise two processes, one displaying an exponential dependence on overpotential and the other only weakly dependent on overpotential. Both interfacial processes displayed near-ideal capacitive behavior, indicating a minimal distribution in the associated relaxation time.