Applied Catalysis B: Environmental, Vol.244, 295-302, 2019
Iridium substitution in nickel cobaltite renders high mass specific OER activity and durability in acidic media
Oxygen evolution reactions being kinetically sluggish and highly expensive remains bottleneck in high pressure hydrogen production from acidic solution water electrolysis. Process economization is mostly affected due to larger consumption of precious iridium as an anodic catalyst. Therefore, effective utilization of noble metal remains a major challenge to be overwhelmed. Comprehensive theoretical and experimental studies show electronic dependency on different structural motifs of IrOx. However, due to lack of suitable non-noble host structures for iridium substitution there is hindrance in implementation. In current study, we explored inverse spinel, nickel cobaltite, as a host structure that provides OER beneficial structural motif to iridium sites on account of relatively higher IrO6 edge sharing than in rutile IrO2. Compact presence of octahedras in host structure reduces Ir-Ir bond length for neighboring IrO6 octahedral units in it that further intrinsically improves the iridium sites due to electronic modulations. Specifically, composite comprising 20 mol% iridium in NiCo2-xO4 rendered acid stable 15 folds enhancement in mass specific OER activity relative to IrO2 resulting in substantial reduction of iridium content. Fabricated composite displayed an onset potential and tafel slope of 1.425 V and 40.4 mV dec(-1), respectively in relative to 1.475 V and 68.1 mV dec(-1) for pure IrO2. Current approach for effectively utilizing precious metal will lead in future for economizing hydrogen production via water splitting.