Enhanced carrier transport in Wurtzite-Sphalerite phase Engineered CdS integrated with CoBOx for High-Performance photoelectrochemical water oxidation

In this work, to dwindle bulk recombination we designed a multi-phase (wurtzite-sphalerite) mCdS (sphere, wire and plate) heterostructure through a novel cation exchange approach. Then customize the mCdS surface with amorphous CoBOx as an oxygen evolution cocatalyst (OEC) to improve the hole utilization and reduce the surface recombination. Plates like mCdS@a-CoBOx photoanodes delivered a significant photocurrent density 1.6 mA cm⁻² at 1.23 V, which is approximately fourfold higher with respect to unmodified mCdS plates. The applied bias photon-current-efficiency of plates mCdS@a-CoBOx also improved two-fold compared to bare mCdS plates. Internal phase junction in mCdS substantially reduces the photoelectron-hole recombination due to the different work functions in wurtzite-sphalerite. Decorated a-CoBOx reduces surface recombination, improves migration, uplifts the electrochemical active surface area, and expedited the hole transfer from CdS to active site a-CoBOx. The structural and chemical characteristics of the photoanode are studied by XRD, XPS, FE-SEM, Cs-TEM and water contact angle. In addition to this, the optoelectronic properties were studied using UV-DRS, Mott-schotty and P-EIS technique. This study paves the way for designing single step synthesis phase junction photoanodes and their OEC modifications to secure high efficiency.