Atomic-Scale Site Engineering Switches HER and CO₂RR on Cu/g‑C₃N₄

Wan-Ting Chen^1*, Hung Wei Shiu¹, Yu-Xun Chen^1,2, Erdembayalag Batsaikhan^3,4, Yu-Ling Lai¹, Su Ling Cheng¹, Tohru Araki⁵, Jyh-Fu Lee¹, Michitoshi Hayashi^3,4,6, Yao-Jane Hsu^1,7

¹Nano Science Group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
³Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
⁴Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, Taiwan
⁵UVSOR Synchrotron Facility, National Institutes of Natural Sciences, Okazaki, Japan
⁶National Center for Theoretical Sciences, National Taiwan University, Taipei, Taiwan
⁷Department of Photonics, National Cheng Kung University, Tainan, Taiwan

* Presenter:Wan-Ting Chen, email:chen.wt@nsrrc.org.tw

Selective electrocatalysis is constrained by competition between the hydrogen evolution reaction (HER) and the CO₂ reduction reaction (CO₂RR). We report a controllable Cu/g-C₃N₄ platform in which metal loading forms single-atoms (Cu-SACs), intercalated dual-atoms (Cu-DACs), or nanoparticles (Cu-NP). We observe that the Cu-SACs and Cu-NPs are HER-dominant (η₁₀ ≈ -0.753 V in 0.5 M H₂SO₄) with no measurable CO₂RR. In contrast, intercalated Cu-DACs, comprising hydrogenated and interlayer Cu sites, enable selective CO₂RR, delivering a Faradaic efficiency for methane of 88% at -0.80 V, while suppressing HER. Under CO₂RR, Cu-DACs exhibit Tafel slopes of 40-53 mV/dec, consistent with a second proton-coupled electron-transfer (PCET) as the rate-determining step. Density-functional theory indicates that interlayer Cu sites stabilize HCOO*/COOH* intermediates and lower the second PCET barrier, consistent with ex situ STXM signatures at low potentials. These results demonstrate atomic-scale site engineering and intercalation as effective levers for directing reaction pathways on a single support. We present a reproducible design rule: loading sets site type, site chemistry governs intermediate binding, and binding dictates selectivity. This yields durable, low-cost, methane-selective CO₂RR catalysts, clarifying the structure-function relationship between atomic configuration, electronic state, and product outcomes.

Keywords: Electrocatalysis, Cu single-atoms catalysts, Cu dual-atoms catalysts, g‑C₃N₄