Alkali metal hydroxide treatment enhances the selectivity of CdWO4 for oxygen reduction to hydrogen peroxide

Abstract

Catalysts with high H₂O₂ selectivity are critical for H₂O₂ electrosynthesis via the 2-electron oxygen reduction reaction (2e⁻ ORR). The carbon-free active centers of transition metal compounds avoid them suffering the performance degradation induced by carbon corrosion, making them potential candidates as long-life catalysts for H₂O₂ electrosynthesis. Nevertheless, the H₂O₂ selectivity of transition metal compounds is generally lower than that of the state-of-the-art metal-free carbon materials and single-atom catalysts. Here, we introduce an alkali metal hydroxide-treatment strategy to improve the H₂O₂ selectivity of tungstate. We synthesized CdWO₄ via a hydrothermal method and soaked the as-prepared CdWO₄ into four types of alkali metal hydroxides (LiOH, NaOH, KOH, and CsOH). It is found that alkali metal hydroxide-treated CdWO₄ exhibited much higher H₂O₂ selectivity than as-prepared CdWO₄, with the CsOH-treated CdWO₄ (denoted as CdWO₄-CsOH) delivering the highest H₂O₂ selectivity and still holding a H₂O₂ selectivity of 93.7% after 40 000 cyclic voltammetry (CV) cycles. Moreover, the CdWO₄-CsOH catalyst retained an average faradaic efficiency (FE) of 84.3% during discharging at 100 mA cm⁻² for 34 h in flow cell tests. Density functional theory (DFT) calculations suggest that W atoms in CdWO₄-CsOH are the preferred active sites for H₂O₂ production.