Oxidation state modulation of CoMOF with Zn for accelerating photoelectrochemical water oxidation of borate-irradiation treated BiVO4

Metal-organic frameworks (MOFs) have been proved to be outstanding catalysts for oxygen evolution reaction (OER). When compared to monometallic MOFs, it's demonstrated that bimetallic MOFs have higher activity and stability. However, the coupling effect of the two metallic ions in bimetallic MOFs is unclear. To clarify the mechanism, bimetallic CoZn-MOFs with OER-inert Zn species are coated on BiVO4 photoanodes. Results show that the oxidation state of Co is improved through the addition of Zn. Combining with borate-irradiation treatment, the CoZnMOF/B-BVO achieves a photocurrent density of 4.27 mA/cm2, which is 3.16 times that of the BVO electrode. Furthermore, the onset potential is negatively shifted by 253 mV, the surface charge injection efficiency is 91% (vs 43.5%, BVO), and the bulk charge separation efficiency reaches 88.2% (vs 51.3%, BVO). The photocurrent of CoZnMOF/B-BVO retains 90% after 10 h test. Oxidation state modulation of MOFs with the second metal is an effective strategy to improve MOFs’ activity.