Tuning Redox Active Polyoxometalates for Efficient Electron‐Coupled Proton‐Buffer‐Mediated Water Splitting

• Published in: Chemistry : a European journal Vol. 25; no. 49; pp. 11432 - 11436
• Main Authors: Lei, Jie, Yang, Jun‐Jie, Liu, Ting, Yuan, Ru‐Ming, Deng, Ding‐Rong, Zheng, Ming‐Sen, Chen, Jia‐Jia, Cronin, Leroy, Dong, Quan‐Feng
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 02.09.2019; John Wiley and Sons Inc
• Subjects: Buffers; Chemistry; Clusters; Communication; Communications; Decoupling; Efficiency; Electrochemistry; Electrolytic cells; electron-coupled proton buffer; Energy efficiency; Energy levels; H2 storage and transportation; polyoxometalates; Polyoxometallates; Protonation; Protons; Redox properties; Redox reactions; Splitting; Water splitting; electron-coupled proton buffer; water splitting; polyoxometalates; H2 storage and transportation
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201903142

We present strategies to tune the redox properties of polyoxometalate clusters to enhance the electron‐coupled proton‐buffer‐mediated water splitting process, in which the evolution of hydrogen and oxygen can occur in different forms and is separated in time and space. By substituting the heteroatom template in the Keggin‐type polyoxometalate cluster, H6ZnW12O40, it is possible to double the number of electrons and protonation in the redox reactions (from two to four). This increase can be achieved with better matching of the energy levels as indicated by the redox potentials, compared to the ones of well‐studied H3PW12O40 and H4SiW12O40. This means that H6ZnW12O40 can act as a high‐performance redox mediator in an electrolytic cell for the on‐demand generation of hydrogen with a high decoupling efficiency of 95.5 % and an electrochemical energy efficiency of 83.3 %. Furthermore, the H6ZnW12O40 cluster also exhibits an excellent cycling behaviour and redox reversibility with almost 100 % H2‐mediated capacity retention during 200 cycles and a high coulombic efficiency >92 % each cycle at 30 mA cm−2. The molecular structure of keggin‐type tungsten polyoxometalates (POMs) were tuned with different heteroatoms to modify their redox properties. Compared to the two electrons of well‐studied H3PW12O40 and H4SiW12O40, H6ZnW12O40 exhibits double reversible electrons with protonation in the redox reactions and the more desirable redox potentials, which enhance its ECPB performance (see scheme).