Surface phosphorization for the enhanced photoelectrochemical performance of an Fe2O3/Si photocathode.

Transition metal phosphates (TMPs) are regarded as efficient co-catalysts for photoanodes, but they are rarely applied in hydrogen production reactions. In this work, iron phosphate (FePi), a co-catalyst for hydrogen production, is introduced onto the Fe2O3 surface by facile surface phosphorization under low-temperature conditions. The surface FePi leads to a shift of the onset potential by +201 mV and an increase in the photocurrent density by more than 10 mA cm-2 at 0 VRHE for the Fe2O3/p-Si photocathode in a strong alkaline electrolyte. The role of FePi stems from the smaller transfer resistance, efficient photogenerated carrier separation and electron injection, and preferable H* adsorption energy, as suggested by Kelvin probe force microscopy and density functional theory (DFT) calculation. The surface phosphorization presents a facile and attractive strategy for the treatment of transition metal oxide catalyzed photocathodes for green hydrogen production.

Coating of Phosphide Catalysts on p-Silicon by a Necking Strategy for Improved Photoelectrochemical Characteristics in Alkaline Media.

The methodology of coating electrocatalysts on semiconductor substrates is critical for the catalytic performance of photoelectrochemical electrodes. A weakly bound coating leads to orders of magnitude lower efficiency and reliability compared to those required to meet the commercial demand. Herein, a facile strategy based on the hydrolysis of TiCl4 is developed to solve the coating issue. Mesoporous tungsten phosphide (WP) particles were spin-coated and affixed onto TiO2-protected planar p-Si by the formation of a TiO2 necking layer between the catalyst particles and the substrates. Under 1 sun illumination, the as-prepared WP/TiO2/Si photocathode yields a saturated current density of -35 mA cm-2 and a durability of over 110 h with a current density over -15 mA cm-2 at 0 V versus a reversible hydrogen electrode in a 1.0 M KOH solution, which is among the state-of-the-art performances of commercial planar Si-based photocathodes. The Kelvin probe force microscopy results suggest the successive transfer of photoelectrons from Si to TiO2 and WP. The as-formed TiO2 necking layer plays the key role in ensuring the surface catalytic activity and durability. This necking strategy is also applicable for coating other transition-metal phosphides, for example, MoP and FeP, thus offering a practical approach to meet the commercial requirement of low-cost, highly efficient, and durable photoelectrodes.