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

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.