A Coordination Polymer Gel as Dual Electrode Material: Photoelectrochemical Water Oxidation Coupled Dark CO$_2$ Reduction to Ethanol

Developing photoelectrochemical catalysts to convert CO2 into chemical feedstocks presents a promising approach for clean energy storage by harnessing solar energy. This study examines the potential of a Zn-based coordination polymer gel (CPG), incorporating terpyridine (TPY) and tetrathiafulvalene (TTF) moieties (Zn-TPY-TTF CPG), for artificial photosynthesis. In this novel approach, Zn-TPY-TTF CPG serves as both photoanode and dark cathode material in a photoelectrochemical (PEC) cell. When combined with BiVO₄ (BVO) nanostructures to fabricate a heterojunction photoanode, Zn-TPY-TTF CPG significantly enhances PEC water-oxidation, delivering a fourfold increase in photocurrent density at 0.6 V versus Ag/AgCl compared to pristine BVO. Kelvin Probe Force Microscopy (KPFM) confirms improved carrier separation and transport due to favorable band alignment between BVO and Zn-TPY-TTF CPG. PEC CO₂ reduction experiments in an H-cell demonstrate a remarkable 43% Faradaic efficiency for ethanol production at 1.4 V versus Ag/AgCl. The simultaneous water-oxidation and CO₂ reduction capabilities of Zn-TPY-TTF CPG position it as a highly promising candidate for solar energy conversion. Operando FTIR and Raman spectroscopy reveal crucial reaction intermediates, while Density Functional Theory (DFT) calculations provide deeper insights into ethanol formation. This study highlights the potential of Zn-TPY-TTF CPG-based PEC cells to mimic natural photosynthesis and produce valuable chemical products.