Cobalt-Based Oxygen Evolution Electrocatalysts Biotemplated on DOPA-Displaying Viruses

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The Oxygen evolution reaction (OER), which involves a more complex mechanism compared to hydrogen evolution reaction (HER), determines the whole cell efficiency for (photo)electrochemical water splitting. Lately, non-precious metal based oxygen evolution catalysts (OECs), such as transition metal oxides got attentions for OER under relatively benign conditions at low overpotentials. In this work, we report a filamentous bacteriophage fd displaying 3,4-dihydroxy-L-phenylanlanine (DOPA) onto the major coat protein and promoted the spontaneous deposition of cobalt oxide based oxygen evolution catalyst (Co-OEC) onto the phages. The virus successfully worked as a biotemplate to enable deposition of thin Co layer along wire-like bodies, and the catechol group of DOPA moiety stabilized Co2+ to accelerate Co-OEC deposition on virus and slightly enhanced OER activity. The Co-based catalysts adhered to DOPA-phages through electroless deposition (Co/DOPA-phages) showed cathodic shift of Co3+/2+ oxidation peak and this phenomenon could be explained from partial-charge transfer from cobalt to DOPA group, which is supported from X-ray photoelectron spectroscopy (XPS) that shows more distinct satellite peaks of Co2+ at ~786 eV compared to electrodeposited Co-OEC. It is widely accepted that partial charge transfer caused by dopant cations raise activity enhancement and change the OER mechanism. The pronounced OER activity under 10 mA cm-2 and long-term stability of Co/DOPA-phages suggest potential for further optimization via systematically ordered and denser array of catechol group for improved performance.