Promoting High-Oxidation-State Metal Active Sites in a Hollow Ternary Metal Fluoride Nanoflake Array for Urea Electrolysis
Ngọc Tuấn Nguyễn, Thuy Tien Nguyen Tran, Thuy‐Kieu Truong, Jianmin Yu, Thong Nguyen‐Minh Le, Thang Bach Phan, Tân Lê Hoàng Đoàn, Linh Hồ Thùy Nguyễn, Tin Dai Luong, Thi‐Hiep Nguyen, Ngoc Quang Tran
Abstract
The adsorption ability of hydrogen, hydroxide, and oxygenic intermediates plays a crucial role in electrochemical water splitting. Electron-deficient metal-active sites can prompt electrocatalytic activity by improving the adsorption ability of intermediates. However, it remains a significant challenge to synthesize highly abundant and stable electron-deficient metal-active site electrocatalysts. Herein, we present a general approach to synthesizing a hollow ternary metal fluoride (FeCoNiF 2 ) nanoflake array as an efficient and robust bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). We find that the F anion withdraws electrons from the metal centers, inducing an electron-deficient metal center catalyst. The rationally designed hollow nanoflake array exhibits the overpotential of 30 mV for HER and 130 mV for UOR at a current density of 10 mA cm –2 and superior stability without decay events over 150 h at a large current density of up to 100 mA cm –2 . Remarkably, the assembled urea electrolyzer using a bifunctional hollow FeCoNiF 2 nanoflake array catalyst requires cell voltages of only 1.352 and 1.703 V to afford current densities of 10 and 100 mA cm –2, respectively, which are 116 mV less compared with that required for overall water splitting.