The Impact of Composition on the Photoelectrochemical Performance of Molybdenum-Modified Tungsten Oxide in Acidic Media

Abstract The efficiency of photoelectrochemical (PEC) water splitting is considerably controlled by the recombination of photogenerated electron/hole charge carriers at the interface. Herein, the correlation between composition and photoelectrochemical activity is studied by utilizing molybdenum-modified tungsten oxide electrodes. Molybdenum tungsten mixed oxides (Mo x W 1− x O 3 ) were synthesized by spray-freeze/freeze-drying approach by varying x from 0 to 1 and studied as a photoanode. The structural changes after Mo substitution in tungsten oxide (Mo x W 1− x O 3 ; 0 ≤ x ≤ 1.0) were observed as a function of the composition. In binary oxides, monoclinic structure (ℽ-phase) was observed until Mo substitution ( x ) reached 0.2. A coexistence of both monoclinic and orthorhombic phases was observed for x varying from 0.2 to 0.8. All synthesized n-semiconducting materials were photoelectrochemically active in water splitting under the acidic condition of HClO 4 . The highest PEC activity was observed for the sample with low Mo content ( x = 0.05) for which the narrowest band gap was determined. The overall activity decrease encountered for Mo-rich materials can be related to a higher tendency to photoinduced proton insertion facilitated by rhombohedral structure. The insight into the mechanism was determined by differential electrochemical mass spectrometry (DEMS). Oxygen ( m / z 32) and hydrogen peroxide ( m / z 34) were identified as main products. The material with small variation in compositions ( x = 0.05) significantly influenced catalytic activity and selectivity, highlighting the importance of the material’s design. Graphical Abstract