CuWO is a photoanode candidate in neutral pH, and manganese-based oxygen evolution reaction electrocatalysts are of high interest due to their low price and low toxicity. Considering the unexplored chemistry of transition-metal carbodiimides/cyanamides for the PEC water oxidation, we investigated MnNCN as an electrocatalyst for CuWO under AM 1.5G illumination in potassium phosphate electrolyte (pH 7). Surface functionalization of CuWO photoanodes with MnNCN increased the photocurrent from 22 to 30 μA cm at 1.23 V vs RHE. Complementary structural analysis by means of XRD and XPS revealed that MnNCN forms a core-shell structure MnNCN@MnPO in phosphate electrolyte and mimics a manganese phosphate electrocatalyst. As such, the surface chemistry of MnNCN significantly differs from previous studies on the cobalt analogue (CoNCN). A separately prepared MnNCN electrode developed a small but detectable photocurrent due to photogenerated holes inside the semiconducting carbodiimide core of the MnNCN@MnPO structure.

We investigated CuWO 4 as a promising photoanode and its surface functionalization with Ag 2 NCN. The composite photoanode displays a synergetic effect between its constituents during photoelectrochemical (PEC) water oxidation. After placing Ag 2 NCN particles on the CuWO 4 thin film, the photocurrent density increases from 15 to 45 μA cm −2 at 1.23 V vs reversible hydrogen electrode (RHE) in phosphate buffer electrolyte at pH 7 under simulated AM1.5 G illumination. The different positions of the band edges of CuWO 4 and Ag 2 NCN favor charge carrier separation at their interface. Upon illumination, photogenerated electrons of both semiconductors are transferred to the conduction band and can migrate to the counterelectrode. The higher position of the conduction band edge of Ag 2 NCN allows its electrons to be injected into the conduction band of CuWO 4 . Simultaneously, holes from the cyanamide are blocked, because the valence band edge position of CuWO 4 is positioned lower than for Ag 2 NCN. This results in more efficient charge separation and hole collection efficiencies. Herein, we emphasize the potential of carbodiimides and cyanamides in the design of photoelectrodes beyond oxide and nitride semiconductors.

Pairing ZnSe/CdS and CdS/ZnSe core/shell quantum dots with NiO thin film photocathodes enhances the photoelectrochemical water reduction.