Excellent electrocatalytic performance of metal-free thiophene–sulfur covalent organic frameworks for hydrogen evolution in alkaline medium

The application of covalent organic frameworks (COFs) for the electrocatalytic hydrogen evolution reaction (HER) has received more attention. However, their poor catalytic performance in alkaline media is problematic for practical application. Herein, we report the synthesis of two metal-free 2D COFs as efficient electrocatalysts for the hydrogen evolution reaction in an alkaline solution. The overpotentials are 136 and 91 at 10 mA cm −2 with small Tafel slopes in alkaline media, respectively. The superior HER activity is due to the thiophene-S units, which have higher conductivity, charge mobility and synergy with one-dimensional nanochannels of 2D COFs. The experimental identification is supported by density functional theory (DFT) calculations. This work demonstrates that rational design of unique thiophene-based COFs can effectively improve their HER activities, which holds great potential for practical applications in water splitting.