Enhanced Photoelectrochemical Water Oxidation Efficiency of CuWO₄ Photoanodes by Surface Modification with Ag₂NCN

Abstract

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.

Nanostructured core–shell metal borides–oxides as highly efficient electrocatalysts for photoelectrochemical water oxidation

“…6,7 Nevertheless, water oxidation involving the transfer of four electrons is demanding with respect to kinetics and stability, thus limiting the PEC watersplitting efficiency. 8,9 Consequently, it is crucial to develop highly active, stable and low-cost photoanodes to achieve commercialization of PEC technology in the future.…”

Nanolayered CuWO4 Decoration on Fluorine-Doped SnO2 Inverse Opals for Solar Water Oxidation

“…Another strategy involved formation of heterojunctions between CuWO 4 and a second semiconductor, such as WO 3 , BiVO 4 , and Ag 2 NCN with synergetic enhancement in photocurrent density. Adam's group used Ag 2 NCN to functionalize the CuWO 4 surface resulting in 3-fold increase in photocurrent density, attributed to more efficient charge separation and hole collection efficiencies under circumstances where the higher position of conduction band edge of Ag 2 NCN favored charge carrier separation at the interface [13]. Similarly, the WO 3 / CuWO 4 photo-anodes show effective band alignment for charge separation from the conduction band edge of WO 3 to CuWO 4 resulting in higher photocurrent.…”

Recent progress of tungsten- and molybdenum-based semiconductor materials for solar-hydrogen production

“…It should be mentioned that the PEC performances in CuWO 4 -based heterojunctions may be mainly contributed from the other coupled semiconductors rather than CuWO 4 itself. Likewise, other CuWO 4 -based heterojunction photoanodes such as CuWO 4 /Ag 2 NCN [179], CuWO 4 /BiVO 4 [180], CuWO 4 /CuO [181], and CuWO 4 /CdS [182] also show enhanced PEC performances. In addition to semiconductors, coupling CuWO 4 with plasmonic metal nanoparticles such as Au and Ag can also improve the PEC performance due to the surface catalytic effect and plasmonic effect [183,184].…”