No abstract

Controlling the selectivity of 4e–/4H+ reduction of oxygen over 2e–/2H+ reduction is a key challenge in making efficient catalysts for fuel cell cathodes. A tyrosine residue poised over the active site of cytochrome c oxidase (CcO) has been demonstrated to control the hydrogen atom transfer reactions and cleavage of the O–O bond of a Fe–O–O–Cu moiety to yield water. In a couple of small-molecule iron complexes supported by porphyrin derivatives, it was shown that the presence of protonation sites at the secondary coordination sphere plays an important role in directing the selectivity and rate of the oxygen reduction reaction (ORR). In this study, we designed and synthesized a mononuclear CoIII complex (1) of a bis-pyridine-bis-oxime ligand where the oxime site can participate in reversible proton exchange reactions. Electrocatalytic ORR of 1 was investigated in aqueous buffer solutions and acetonitrile containing trifluoroacetic acid as the proton source. We observed that in a 0.1 M phosphate buffer solution (PBS), 1 is selective for 4e–/4H+ reduction of O2 at pH 4, and the selectivity decreases with increasing the buffer medium’s pH, producing ca. 75% H2O at pH 7. However, in a 0.1 M acetate buffer solution (ABS), 1 remained highly selective for the cleavage of the O–O bond to produce H2O at pH 4 and pH 7. The overpotential (η) of H2O formation (ca. 0.8–0.65 V) decreased proportionally with increasing pH in PBS and ABS. In acetonitrile, 1 remained highly selective for 4e–/4H+ reduction for electrocatalytic and chemical ORR. An overpotential of 760 mV was estimated for H2O production in acetonitrile. Kinetic analysis suggests the first-order dependence of catalyst concentration on the reaction rate at 25 °C. However, the formation of a peroxo-bridged dinuclear cobalt­(III) complex was noted as a reaction intermediate in the ORR pathway in acetonitrile at −40 °C. We conjecture that the oxime scaffold of the ligand works as a proton exchanging site and assists in the proton-coupled electron transfer (PCET) reactivity to cleave the O–O bond in the acidic buffer solutions and acetonitrile, further corroborated by theoretical studies. Density functional theory (DFT) calculation suggests that the acetate ion works as a mediator at pH 7.0 for transferring a proton from the oxime scaffold to the distal oxygen of the CoIII(OOH) intermediate, responsible for high selectivity toward 4e–/4H+ reduction of O2.

Prussian blue analogues (PBAs), due to their high surface area, large density of catalytically active sites, and high porosity, are one of the potential bifunctional oxygen electrocatalysts for industrial applications. However, so far, only limited success has been achieved toward developing highly efficient PBA-based electrocatalysts. Therefore, unravelling the underlying structure–property–activity relationship and designing strategies or combination of tested strategies are crucial to this effect. In this work, we demonstrate a strategy to concurrently engineer the coordination sphere vacancies and Lewis acid sites, via atomically dispersed Zn2+ dopants in CoFe PBA that makes Co n+ more electropositive, to boost the bifunctional oxygen electrocatalysis on PBA surfaces. The optimal Zn-doping (3 mole %) not only enhances the oxygen evolution reaction (OER) activity of CoFe PBAs to the comparable level of the IrO2 catalyst but also depicts an impressive bifunctional oxygen activity with a low reversible overvoltage of 0.84 V. This work also demonstrates that an in situ formation of Co3+ (CoOOH) and Fe3+ (FeOOH) during the OER plays a crucial role for the boosted activity in bifunctional oxygen electrocatalysis. Besides providing highly efficient and low-cost catalysts, this study also imparts important insights to improve the efficiency of PBA-based bifunctional oxygen electrocatalysis.

Development of an efficient non-precious metal-based bi-functional oxygen electro-catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for various electrochemical energy conversion and storage devices. Prussian...

Purpose “Paying for performance” has been the corporate mantra for ages, but finding the right performance benchmarks continues to be an enigma. Equally significant is the ongoing debate on the superiority of economic value added (EVA) aligned executive incentive plans over traditional financial performance benchmarks to ensure optimal goal congruence between the corporate and the executive performances. Consequently, this paper aims to explore a plausible linkage between executive compensation and EVA for Indian corporates from a social constructivist perspective. Design/methodology/approach The study uses a mixed method approach where the quantitative analysis of responses from the survey of senior personnel/finance executives of Indian firms is complemented by the qualitative analysis of personal interviews to provide contextual depth to the quantitative data. Findings Based on the study, the researchers construct an understanding that EVA is a superior concept but has restricted utility primarily owing to its computational complexity and unaudited characteristics. The researchers’ interpretive inference finds mandatory disclosure of an audited EVA figure in the corporate financial statements as a prime requirement for EVA to emerge as an objective and visible performance measure. Practical implications Attention of policymakers is sought towards standardising its computation and ensuring its disclosure to bring it at par with the conventional executive financial performance benchmarks. Originality/value The narrative on benefits and the challenges of adopting EVA aligned performance management system is provided directly by the top-level executives responsible for designing the “paying for performance” policies.