Design and Development of Efficient Bifunctional Catalysts by Tuning the Electronic Properties of Cobalt–Manganese Tungstate for Oxygen Reduction and Evolution Reactions

• Published in: ChemCatChem Vol. 9; no. 19; pp. 3681 - 3690
• Main Authors: Karkera, Guruprakash, Sarkar, Tanmay, Bharadwaj, Mridula Dixit, Prakash, Annigere. S.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 10.10.2017
• Subjects: bifunctional catalysts; Carbon dioxide; Catalysts; Catalytic activity; Cobalt; Current density; Electrochemistry; Electron transfer; Energy conversion; Energy storage; Fermi surfaces; Hydrogen storage; Manganese; metal tungstates; Oxygen evolution reactions; oxygen reduction reactions; Planes; Solid solutions; Surface energy; Tuning
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201700540

Solid‐state electrochemistry is drawing considerable interest as the interconversion of O2 and water playing an important role in energy conversion and storage technologies. With the aim of developing an efficient bifunctional catalyst by tuning the electronic properties and local structure around the 3d metal in CoWO4, solid solutions of Co1−xMnxWO4 are investigated. Nanocrystalline Co1−xMnxWO4 (x=0 to 1) phases with a unique exposure of low surface energy planes are synthesized by hydrothermal methods. Replacing an optimum amount of Co with Mn to enhance the catalytic activity leads a observation of a negative shift in the Co2+/3+ redox wave and onset of the oxygen evolution reaction (OER), indicating a strong electronic interaction between the two elements. The composition corresponding to Co0.5Mn0.5WO4 has demonstrated great ability to catalyze both the OER and oxygen reduction reaction (ORR) with a combined overpotential of 0.89 V. It exhibited an OER current density of 10 mA cm−2 at an overpotential of 400 mV. Whereas ORR current density of 3 mA cm−2 is reached at a potential of 0.74 V versus reversible hydrogen electrode (RHE). The density functional theory revealed that the substitution of Mn in CoWO4 elevate the 3d metal d band center closer to the Fermi energy and hence ease the electron transfer to facilitate ORR and OER. Defects are the key! The schematic representation of electronic states in MWO4 (M=Co, Mn) and their solid solution to show Co/Mn d, O p, and W d band centers in cobalt–manganese tungstates as an efficient bifunctional catalyst for oxygen reduction and evolution reactions.