Switching the O–O bond-formation mechanism by controlling water activity

The O–O bond-formation mechanism in water oxidation is still ambiguous even now. In this issue of Chem, Wang and co-workers prove that on a Co-based electrocatalyst can switch from radical coupling pathway to nucleophilic attack when the applied potential lifted. oxygen evolution reaction (OER) paramount significance area solar energy conversion. It initial step photosynthesis produce dioxygen for supporting aerobic life liberate electrons protons as carriers. Meanwhile, next-generation revolution based electrochemistry, it key anode series energy-related small-molecule activations (hydrogen production, carbon dioxide reduction, nitrogen so forth) driven by sustainable electricity.1Zhang X.-P. H.-Y. Zheng H. Zhang W. Cao R. bond formation mechanisms during over synthetic molecular catalysts.Chin. J. Catal. 2021; 42: 1253-1268Crossref Scopus (44) Google Scholar OER very complicated because its multiple diverse proton-coupled electron-transfer fundamental steps, including kinetically challenging step. With decades research, oxygen-evolving center (OEC) nature under debate. This important process has inspired chemists develop wealth catalytic motifs order understand mechanism. However, not fully understood homogeneous catalysts with well-defined structures—not mention heterogeneous systems more uncertainties structures surface centers.2Zhang Chandra A. Lee Y.-M. Ray K. Nam Transition metal-mediated O-O activation chemistry biology.Chem. Soc. Rev. 50: 4804-4811Crossref PubMed probe electrocatalysts innovatively changing activity water-in-salt electrolytes.3Lang C. Li Yang K.R. Y. He D. Thorne J.E. Croslow S. Dong Q. Zhao Prostko G. et al.Observation potential-dependent Co-oxide-based catalysts.Chem. 7: 2101-2117https://doi.org/10.1016/j.chempr.2021.03.015Abstract Full Text PDF (16) They discovered water-oxidation might an intramolecular (RC) at low potentials predominant nucleophilic-attack acid-base (AB) higher potentials. Specifically, resting state catalyst HO–Co(III)–(μ-O)2–Co(IV)–OH intermediate. hydroxide partial character undergo form hydroperoxide via RC relatively At potentials, above-mentioned intermediate be further oxidized into O=Co(IV)–(μ-O)2–Co(IV)–OH motif. terminal electrophilic oxo O=Co(IV)– participate through AB addition, authors believe barrier function electrode given one substances (water) large dipole moment, dynamics electrified interfaces could strongly depend potential. thermodynamically favored whereas polarization cause predominance pathway. To elucidate different cleverly controlled using electrolytes. adjusted 1 0.83 NaNO3 concentrations 0.1 M KPi buffer neutral pH. observed decrease rate decreased range 1.61–1.71 V (versus reversible hydrogen [RHE]; all refer RHE hereafter). factor ∼1.2 1.615 0.83. Interestingly, rate-suppression dramatically increased ∼4.3 1.71 V. distinctive suppression factors indicate molecules are less likely involved rate-determining (RDS) participates RDS substance high observation corroborates also tested kinetic isotope effect (KIE) heavy KIE values ∼2 ∼4.2 1.625 V, respectively. was insensitive H/D substitution, but highly involve transfer RDS. experiment consolidates their conclusion switches reported surface-enhanced infrared absorption spectroscopy (SEIRAS) Au substrate isotopic labeling experiments insinuate presence Co superoxide which supported proposed cycles certain extent. addition evaluating how altering affects formation, performed comprehensive well-designed control tightly bridge findings conclusions. excluded any irreversible changes, effects limited mass transport, Na+ salts, transition-metal impurities system; they confirmed concentration salts did significantly affect local pH or block sites interface; showed near-unity faradic efficiency dioxygen. exact experimental design rigorous analysis data electrocatalytic extremely happening intricate interface. Unlike systems, where well defined, ambiguous.4Yang X. C.M. Mechanisms surfaces.Nano Res. https://doi.org/10.1007/s12274-021-3607-5Crossref (21) rates electrocatalysis affected variety factors, interferences should eliminated origins activities assigned.5Trotochaud L. Young S.L. Ranney J.K. Boettcher S.W. Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: role intentional incidental iron incorporation.J. Am. Chem. 2014; 136: 6744-6753Crossref (2130) following aspects recommended regarding studies. First, better find specific structure, structure stable conditions. Second, exclude possible interference, platforms comparison studies straightforward differences counterparts many physical varieties. Third, behaviors followed special attention paid details include minor easily ignored have considerable impact performance.6Wei Rao R.R. Peng J.Y. Huang B.T. Stephens I.E.L. Risch M. Xu Z.C.J. Shao-Horn Recommended practices benchmark splitting fuel cells.Adv. Mater. 2019; 31: 1806296Crossref (541) Particularly, some inherent connections OEC bearing Mn-based complex nature. early transition metals (Ti, Cr) M=O units late (Ni Cu) only theoretically unstable structures, metal-oxo motif Mn, Fe, between two valence tautomers Mn+1=O2– Mn–O•–.2Zhang former atom proceed bond, latter favors formation. pathways believed concurrent necessary point out metal-oxide-based usually lattice atoms coupling. authors, HO–Co(III)– unit too –Co(IV)–OH character. bridged atoms, generally nature.7Najafpour M.M. Renger Hołyńska Moghaddam A.N. Aro E.-M. Carpentier Nishihara Eaton-Rye J.J. Shen J.-R. Allakhverdiev S.I. Manganese compounds water-oxidizing catalysts: natural nanosized manganese oxide structures.Chem. 2016; 116: 2886-2936Crossref (461) Overall, thought provoking biological process. Observation catalystsLang al.ChemApril 14, 2021In BriefThe elementary reaction, dependence remains ambiguous. Using electrolyte, we systematically tuned probed We found sensitive forms proceeds Full-Text Open Archive