In situ observations of oxygen evolution Cocatalysts on Photoelectrodes by x-ray absorption spectroscopy: Comparison between cobalt-phosphate and cobalt-borate

The differing activities of cobalt-phosphate (Co-Pi) and cobalt-borate (Co-Bi) oxygen evolution cocatalysts photodeposited on SrTiO3 photoelectrodes under the same conditions for use in water splitting were investigated using in situ X-ray absorption fine structure (XAFS) spectroscopy. Prior to XAFS analyses, the photoelectrochemical water oxidation activities of both cocatalysts were assessed by linear sweep voltammetry, with results demonstrating that the Co-Bi cocatalyst enhances oxygen evolution to a greater degree than the Co-Pi. Co Kedge XAFS spectra were acquired for both cocatalysts on SrTiO3 photoelectrodes during photoelectrochemical water splitting. The XAFS spectrum of the Co-Bi was significantly more intense than that of the Co-Pi, indicating that a greater concentration of the Co-Bi cocatalyst was present on the photoelectrode compared with the Co-Pi. The results of this study demonstrate that both the Co-Pi and Co-Bi cocatalysts are able to efficiently promote water oxidation, and that the Co-Bi functions more effectively than the Co-Pi because it generates a greater abundance of reaction sites.