Electrochemical hydrogen evolution reaction (HER) coupled with renewable energy is a promising way to produce green hydrogen. Pt is the well-known best metal electrocatalyst for HER, but the commercial application is limited by its scarce resources. Various Pt single-site catalysts (SSCs) with 100% Pt atom utilization have been developed to minimize the use of Pt in recent years. Among them, Pt SSCs supported on N-doped carbon (Pt-N-C) show excellent dispersion and activity, yet the HER mechanism on them remains unclear. Therefore, it is crucial to peoferom theoretical simulations under electrocatalytic working conditions to elucidate reaction mechanisms and the origin of activity.
Recently, the research group of professor Zheng Hu at the Key Laboratory of Mesoscopic Chemistry of MOE has systematically simulated the thermodynamics and kinetics of HER on 19 typical Pt-N-C sites by a CEP first-principles method with the multi-H-atom adsorption modes, in association with the working conditions of electrode potential and acidic aqueous environ-ment. The unique H adsorption mode on these sites make the HER routes quite different from traditional knowledge. Four highly active struc-tures, namely PtN2, PtN2C, PtNC2 and 2-PtNC2V, were identified, and they share a common feature of Hδ- with near zero adsorption energy. The Hδ- is formed on the para position of C or H ligands and stabilized by N ligands, which can quickly combine with a proton to produce H2 due to the favorable electrostatic attraction. Moreover, the Volmer/Heyrovsky-dominated, rather than the generally-accepted Tafel-dominated, HER mechanism is demonstrated for Pt-N-C SSCs. This study provides a new indicator of Hδ- with near zero adsorption energy to design highly active HER metal SSCs, with a deep insight into the HER mechanism of Pt SSCs.
Figure 1 Typical structures of Pt-N-C SSCs and possible HER steps. (a) Schematic structures of Pt-N-C SSCs. (b, c) Schematic HER steps for single-H-atom adsorption (b) and multi-H-atom adsorption (c).
Figure 2 The H adsorption structures and HER paths on PtX2 single sites. (a) The free energy curves of the multiple H adsorption processes on PtX2 single sites. (b-c) The H adsorption structures and the HER paths on PtC2 (b)and PtN2 (c). (d) The ΔG≠s along the HER paths on PtC2 and PtN2. (e) The electronic arrangement of typical adsorption structures on PtC2, PtNCand PtN2.
Figure 3 The H-adsorption structures and HER paths on PtX3 single sites. (a) The free energy curves of the multiple H adsorption processes. (b) The ΔG≠s along the HER paths on PtN2C and PtNC2. (c-d) The H adsorption structures and the HER paths on PtN2C (c)and PtNC2 (d).
Figure 4 The H-adsorption structures and HER paths on PtX4 and PtX3V single sites. (a-b) The free energy curves of the H adsorption processes on PtX4 (a) and PtX3V (b) single sites. (c) The H adsorption structures and the HER paths on PtN3V, 1-PtN2CV, 1-PtNC2Vand 2-PtNC2V. (d) TheΔG≠s along the HER paths on PtN3V, 1-PtN2CV, 1-PtNC2Vand 2-PtNC2V.
Figure 5 Relationship between the barriers of H2 formation and the charges carried by the adsorbed H on the Pt-N-C sites. (a-d) Charges carried by the adsorbed H atoms on the four highly active structures. (e) The adsorption energy of Hδ- in (a-d) taken from Figure 2-4. (f) The relationship between the barrier of H2 formation and the charge carried by the adsorbed H atom involved in this step. (g) The relationship between the Pauling electronegativity of the ligand and the Mulliken charge carried by the adsorbed H atom on its para/ortho position.
The related paper entitled “Volmer/Heyrovsky-Dominated Hydrogen Evolution on Pt-N-C Single Sites Triggered by Negatively-Charged Adsorbed Hydrogen: A Theoretical Insight” has been published on ACS Catalysis on June12, 2025 (Paper link: https://doi.org/10.1021/acscatal.5c02724, DOI:10.1021/acscatal.5c02724). Ph.D. student Chenghui Mao is the first author.Prof. Lijun Yang and Prof. Zheng Hu from our department are co-corresponding authors. This work was jointly supported by the National Key Research and Development Program of China (No. 2021YFA1500900), the National Natural Science Foundation of China (Nos. 52071174), the Natural Science Foundation of Jiangsu Province, Major Project (BK20212005) and the Foundation of Science and Technology of Suzhou (No. SYC2022102).