Single-atom Ir and Ru anchored on graphitic carbon nitride for efficient and stable electrocatalytic/photocatalytic hydrogen evolution

Renewable energy-powered water electrolysis and photocatalytic water splitting are two promising approaches to green hydrogen production. Electrocatalysts and photocatalysts are essential components determining the performance of water electrolyzers and photocatalytic reactors, respectively. Currently, there is a pressing need to develop efficient and stable electrocatalysts and photocatalysts for large-scale deployment of these devices to reach carbon neutrality. Herein, we report the synthesis of single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (Ir-g-CN and Ru-g-CN), which can be used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER). Remarkably, Ru-g-CN shows a high turnover frequency (TOF) of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming Ir-g-CN, commercial Pt/C benchmark and many other advanced HER catalysts reported recently. Moreover, Ru-g-CN can deliver an exceptionally high mass activity of 24.55 and 8.78 A mg−1 at η = 100 mV in acidic and alkaline solutions, meanwhile exhibiting a high apparent current density, which is favorable for practical applications. Additionally, both Ru-g-CN and Ir-g-CN show outstanding catalytic stability, continuously catalyzing the HER in acidic and alkaline conditions for 120 h with minimal degradation. Besides, when used for photocatalytic water splitting, Ru-g-CN can achieve a high hydrogen production rate of 489.7 mmol H2 gRu−1 h−1, and shows good photocatalytic stability. Our density functional theory (DFT) calculations demonstrate that loading Ir and Ru single-atoms on g-CN alters the electronic structure, resulting in a reduced bandgap and improved electrical conductivity, facilitating electron transfer during the catalysis. Moreover, the Gibbs free energy of hydrogen adsorption on Ru-g-CN and Ir-g-CN is also substantially lowered, enhancing HER performance.