Tethering Cobalt Ions to BiVO 4 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 BiVO 4 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 BiVO 4 and utilized to tether cobalt ions. The Co-DPAA/BiVO 4 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 BiVO 4 , DPAA/BiVO 4 , Co-BiVO 4 , and Co-Pi/BiVO 4 photoanodes, respectively. The photoelectrochemical and IMPS studies revealed that the Co-DPAA/BiVO 4 photoanode exhibits a longer transient decay time for surface-trapped holes, higher charge transfer kinetics, and charge separation efficiency compared to Co-Pi/BiVO 4 and pristine BiVO 4 photoelectrodes. This indicates that the Co-DPAA effectively reduces surface recombination and facilitates charge transfer. Moreover, at 1.23 V RHE , the Co-DPAA/BiVO 4 photoanode achieved a faradic efficiency of 92% for oxygen evolution reaction and could retain a turnover frequency of 3.65 s -1 . The- exhibited effeciency is  higher than most of the efficient molecular oxygen evolution catalyst based on Ru.