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

Abstract

Catalysts with high H 2 O 2 selectivity are critical for H 2 O 2 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 H 2 O 2 electrosynthesis. Nevertheless, the H 2 O 2 selectivity of transition metal compounds are generally lower than the state-of-the-art metal-free carbon materials and single-atom catalysts. Here, we introduce an alkali metal hydroxides-treatment strategy to improve the H 2 O 2 selectivity of tungstate. We synthesized CdWO 4 via a hydrothermal method and soaked the as-prepared CdWO 4 into four types of alkali metal hydroxides (LiOH, NaOH, KOH, and CsOH). It is found that alkali metal hydroxides-treated CdWO 4 exhibited much higher H 2 O 2 selectivity than as-prepared CdWO 4 , with the CsOH-treated CdWO 4 (denoted as CdWO 4 -CsOH) delivering the highest H 2 O 2 selectivity and still holding a H 2 O 2 selectivity of 93.7% after 40,000 cyclic voltammetry (CV) cycles. Moreover, the CdWO 4 -CsOH catalyst maintained an average Faradaic efficiency (FE) of 84.3% during discharging at 100 mA cm -2 for 34 h in flow cell tests. X-ray photoelectron spectroscopy (XPS) results indicate that a higher binding energy of W may be responsible for the H 2 O 2 selectivity improvement of alkali metal hydroxides-treated CdWO 4 in comparison to as-prepared CdWO 4 .