Construction of ternary TiO ₂ /CdS/IrO ₂ heterostructure photoanodes for efficient glycerol oxidation coupled with hydrogen evolution

A TiO₂/CdS heterostructure has been widely investigated as a potential photoanode for photoelectrochemical (PEC) water splitting for hydrogen evolution. However, the efficiency and stability still remain challenging due to the sluggish reaction dynamics for water oxidation and easy photocorrosion of CdS. Here we report a ternary TiO₂/CdS/IrO₂ heterostructure with IrO₂ as a hole transport layer for PEC glycerol oxidation coupled with hydrogen evolution. The photocurrent density of the optimized TiO₂/CdS photoanode is 18.8 mA cm^-2 (1.23 V <i>vs</i>. RHE), which is about 10.6 times higher than that of the pristine TiO₂. It is found that most of the glycerol was converted to formic acid (FA) on the TiO₂/CdS surface with a production rate of ∼603.0 mmol m^-2 h^-1. The average H₂ production rate reaches 1574.5 mmol m^-2 h^-1. After loading IrO₂ nanoparticles, the products for glycerol oxidation remain unchanged with the production rate of FA reaching 863.4 mmol m^-2 h^-1, while the hydrogen production rate is increased to 2345.2 mmol m^-2 h^-1 due to the improved stability. The results show that the obtained TiO₂/CdS/IrO₂ heterostructure can effectively oxidize glycerol to value-added chemicals. The enhanced PEC performance and stability of the TiO₂/CdS/IrO₂ photoanode can be ascribed to the greatly enhanced electrode/electrolyte interfacial carrier injection efficiency, caused by the fast glycerol oxidation dynamics and intimate contact. This work provides novel ideas to construct high-efficiency PEC systems for both clean energy production and high-value chemicals.