Feed water quality is the primary cause for stack failure in commercial water splitting electrolyzers. It is therefore of paramount importance to develop and demonstrate water quality-resilient electrocatalysts that maintain high activity, selectivity, and stability in complex nonideal electrolytic environments. This becomes particularly challenging and notable for the kinetically hindered four-electron transfer anodic oxygen evolution reaction (OER), especially in brackish and sea waters due to the undesired competing chlorine evolution reaction (CER). Not only is CER of concern in these complex water systems, but also the presence of calcium and magnesium species, which form precipitates in alkaline pH electrolyte causing passivation of catalytically active sites and fouling of membrane dividers. To avoid formation of these precipitates, neutral and near-neutral pH operation is desired. However, this mode of operation further hampers the OER kinetics due to the requirement of an initial water dissociation step. Herein, we developed a homogenous surface heterointerfaced Co-(NiFe) oxide/nitride active layer atop an interlaying NiSx grown on porous nickel foam substrate. The optimum Co-(NiFe)N@NiSx@NF electrocatalyst enhanced water dissociation kinetics and selectivity towards OER during high current density operation, consequently activating typically limited neutral-pH performance and stability. This translated to the best performing anode attaining 100 mA cm-2 of current density at low overpotentials of 350 and 430 mV in alkaline and neutral pH synthetic seawater electrolytes. Further, in situ gas chromatography analysis yielded 94.5 and 88.6% OER Faradaic efficiencies in alkaline and neutral pH synthetic seawater electrolyte for the same NiSx interlayered sample. Thereby the attained performance suggests that electrocatalysts designed towards neutral-pH can in fact be tailored to achieve similar electrochemical performance to their alkaline pH counterparts. Characterization techniques including, but not limited to, HRTEM, XAS, XPS, XRD, and electrochemical analyses were utilized to convey the intrinsic properties of the developed catalysts and their electrochemical performance.

Surface heterointerfaced Co-(NiFe) oxide/nitride with NiSx interlayers towards oxygen evolution reaction in neutral pH environments

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