Abstract
Ag(I) is commonly employed as an electron scavenger to promote water oxidation. In addition to its straightforward role as an electron acceptor, Ag(I) can also capture holes to generate the high-valent silver species. Herein, we demonstrate photoelectrocatalytic (PEC) water oxidation and concurrent dioxygen evolution by the silver redox cycle where Ag(I) acts as a hole-transfer mediator. Ag(I) enhances the PEC performance of WO3 electrodes at 1.23 V vs. RHE with increasing O2 evolution, while forming Ag(II) complexes (AgIINO3+). Upon turning off both light and potential bias, the photocurrent immediately drops to zero, whereas O2 evolution continues over ~10 h with gradual bleaching of the colored complexes. This phenomenon is observed neither in the Ag(I)-free PEC reactions nor in the photocatalytic (i.e., bias-free) reactions with Ag(I). This study finds that the role of Ag(I) is not limited as an electron scavenger and calls for more thorough studies on the effect of Ag(I).
Highlights
Ag(I) is commonly employed as an electron scavenger to promote water oxidation
Small photocurrent spikes appeared in the presence of AgNO3 (Supplementary Fig. 4), likely due to the sudden release of oxygen bubbles from the WO3 surface
The accompanying O2 evolution increased with irradiation time, leading to the Faradaic efficiency (FE) of ~75%, while the solution acquired a brown color, likely caused by the formation of AgIINO3+ complex[20,21,30,31]
Summary
Ag(I) is commonly employed as an electron scavenger to promote water oxidation. In addition to its straightforward role as an electron acceptor, Ag(I) can capture holes to generate the high-valent silver species. The accompanying O2 evolution increased with irradiation time (over four times higher than that in the absence of AgNO3), leading to the FE of ~75% (for 3 h), while the solution acquired a brown color, likely caused by the formation of AgIINO3+ complex (see Fig. 1b inset)[20,21,30,31]. Such O2 evolution during the post-PEC period was not observed in the presence of persulfate (Na2S2O8), a well-known electron scavenger (Supplementary Fig. 5), which indicates the unique role of Ag+.
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