Kuei-Hsien Chen

The electrocatalytic carbon dioxide reduction reaction (eCO2RR) in an acidic environment is crucial for mitigating carbonate and bicarbonate formation while enhancing CO2 conversion efficiency. However, the hydrogen evolution reaction (HER) often outcompetes eCO2RR in a proton-rich microenvironment, posing a significant challenge. This study introduces an in-situ phosphatizing method to alter the electronic structure of a Ni–N4 single-atom catalyst (Ni–N3PC), thereby suppressing HER and promoting eCO2RR performance in acidic environments. The Ni–N3PC catalyst achieves a CO Faradaic efficiency (FE) exceeding 90 % over a wide potential range, high carbon conversion efficiency, a CO partial current density of –357.7 mA cm−2, and long-term stability for 100 h at –100 mA cm−2 with a FE of 85 %. Electrochemical impedance spectroscopy and turnover frequency analysis reveal that Ni–N3PC exhibits lower charge-transfer resistance and higher intrinsic activity, respectively. The structural characterization using X-ray absorption spectroscopy confirms the formation of Ni–P and Ni–N bonds while scanning transmission electron microscopy shows atomically dispersed Ni atoms on carbon networks. Density functional theory calculations further support the experimental results, showing that Ni–N3PC significantly lowers the energy barrier for the key *COOH intermediate, resulting in outstanding eCO2RR performance. This research provides valuable insights into the design of highly efficient Ni single-atom catalysts for industrial eCO2RR applications.

Exploring an efficient platinum group metal (PGM) free electrocatalyst with superior activity and stability for hydrogen evolution reaction (HER) in a wide pH range is desirable for low-cost hydrogen production. Here, we report atomically dispersed cobalt on nitrogen and sulfur co-doped graphene (N-Co-S/G) for HER. Remarkably, the prepared N-Co-S/G electrocatalyst shows a small overpotential of 67.7 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2 and exceptional durability over 100 h at 10 mA cm−2 under acidic conditions. Moreover, we found that the HER activity of N-Co-S/G is close to 20% Pt/C at all pH levels (0–14) and superior activity at high current density (>100 mA cm−2). Experimental and theoretical calculations reveal that the S atom in N-Co-S/G form Co-S bond, resulting new Co-N3S1 active site, which optimizes Gibbs free energy for hydrogen adsorption (∆GH*) close to zero, while water adsorption and dissociation enhanced by S modulation for neutral and basic media HER.