Hao Tian

Electrocatalytic reduction of CO₂ to CH₄ is a promising strategy for converting renewable energy into a desirable high-energy-density fuel with significant compatibility with the existing natural gas infrastructure. However, conventional alkaline and neutral CO₂-to-CH₄ systems exhibit low carbon utilization due to the loss of CO₂ into (bi)carbonate. Conducting CO₂ electroreduction in acid can alleviate carbonation issues but suffers from moderate CH₄ selectivity owing to competing hydrogen evolution. Herein, we report that thiocyanate (SCN^-), a well-known poison in electrocatalysis, can remarkably enhance acidic electrocatalytic CO₂-to-CH₄ performance, specifically resulting in a record-high CH₄ Faradaic efficiency of 81.8% (accompanied by a CH₄ partial current density of 213.3 mA cm^-2) and a single-pass carbon efficiency of 65.2% when using a CeO₂-supported Cu single-atom material as the model catalyst. We demonstrate that SCN^- enables the coordination with Cu single sites, forming the SCN^--stabilized Cu^(I) species, which effectively suppresses the competing hydrogen evolution reaction and, more importantly, manipulates the binding of *CHO to promote its protonation to *CHOH, thereby leading to selective and efficient CH₄ production. This work highlights the unique role of thiocyanate in promoting the selective reduction of CO₂ to CH₄ and offers insights into the design of surface chemistry for precise regulation of catalytic processes to achieve targeted product production.

Water molecules linked by hydrogen bonds are responsible for the high efficiency of bi-functional catalysts for the water-gas-shift (WGS) reaction because water can act as a proton transfer medium. Herein, we propose an associative pathway for the WGS reaction assisted by water to realize hydrogen production. Based on this pathway, we show by first-principles calculations that a large family of oxygen-terminated two-dimensional transition metal carbides and nitrides (MXenes) deposited on Au clusters are promising catalysts for the WGS reaction. Remarkably, the rate-determining barriers for *CO → *COOH on Au/M_n+1X_nO₂ are in the range from 0.15 eV to 0.39 eV, indicating that WGS can occur at much lower temperatures. Furthermore, a comprehensive microkinetic model is constructed to describe the turnover frequencies (TOF) for the product under the steady-state conditions. More importantly, there is a perfect linear scaling relationship between the rate-determining barriers of the WGS and the free energy of the adsorbed hydrogen. Besides, the potential energy diagrams for CO reforming reveal that the F terminations introduced in experiments have only a slight influence on the catalytic performance of the oxygen-terminated MXenes. Our work not only opens a new avenue towards the WGS reaction but also provides many ideal catalysts for hydrogen production.

Confining interacting particles in one-dimension (1D) changes the electronic behavior of the system fundamentally, which has been studied extensively in the past. Examples of 1D metallic systems include carbon nanotubes, quasi-1D organic conductors, metal chains and domain boundary defects in monolayer thick transition-metal dichalcogenides such as MoSe₂. Here single and bundles of Mo₆Se₆ nanowires were fabricated though annealing MoSe₂ monolayer grown by molecular-beam epitaxy on graphene. Conversion from two-dimensional (2D) MoSe₂ film to 1D Mo₆Se₆ nanowire is reversible. Mo₆Se₆ nanowires form preferentially at the Se-terminated zigzag edges of MoSe₂ and stitch to it via two distinct atomic configurations. Mo₆Se₆ wire is metallic and its length is tunable, which represents one of few ideal 1D systems that exhibit properties pertinent to quantum confined Tomonaga-Luttinger liquid, as evidenced by scanning tunneling microscopic and spectroscopic studies.