Tethering Cobalt Ions to BiVO₄ Surface via Robust Organic Bifunctional Linker for Efficient Photoelectrochemical...

In the quest for efficient and stable oxygen evolution catalysts (OECs) for photoelectrochemical water splitting, the surface modification of BiVO₄ is a crucial step. In this study, a novel and robust OEC, based on 3-(bis(pyridin-2-ylmethyl) amino) propanoic acid bifunctional linker known as dipicolyl alanine acid (DPAA) and cobalt ions, is prepared and fully characterized. The DPAA is anchored to the surface of BiVO₄ and utilized to tether cobalt ions. The Co-DPAA/BiVO₄ photoanode exhibits remarkable stability and efficiency toward photoelectrochemical water oxidation. Specifically, it showed anodic photocurrent increase of 7.1, 5.0, 3.0, and 1.3-fold at 1.23 V_RHE as compared to pristine BiVO₄, DPAA/BiVO₄, Co-BiVO₄, and Co-Pi/BiVO₄ photoanodes, respectively. The photoelectrochemical and IMPS studies revealed that the Co-DPAA/BiVO₄ photoanode exhibits a longer transient decay time for surface-trapped holes, higher charge transfer kinetics, and charge separation efficiency compared to Co-Pi/BiVO₄ and pristine BiVO₄ photoelectrodes. This indicates that the Co-DPAA effectively reduces surface recombination and facilitates charge transfer. Moreover, at 1.23 V_RHE, the Co-DPAA/BiVO₄ photoanode achieved a faradic efficiency of 92% for oxygen evolution reaction and could retain a turnover frequency of 3.65 s^-1. The exhibited efficiency is higher than most of the efficient molecular oxygen evolution catalysts based on Ru.