Electrochemical CO₂-reduction reaction (CO₂RR) is a promising way to alleviate energy crisis and excessive carbon emission. The Cu-based electrocatalysts have been considered for CO₂RR to generate hydrocarbons and alcohols. However, the application of Cu electrocatalysts has been restricted by a high onset potential for CO₂RR and low selectivity. In this study, we have designed a series of Cu-based single-atom alloy catalysts (SAAs), denoted as TM₁/Cu (111), by doping isolated 3d-transition metal (TM) atom onto the Cu (111) surface. We theoretically evaluated their stability and investigated the activity and selectivity toward CO₂RR. Compared to the pure Cu catalyst, the majority TM₁/Cu (111) catalysts are more favorable for hydrogenating CO₂ and can efficiently avoid the hydrogen-evolution reaction due to the strong binding of carbonaceous intermediates. Based on the density functional theory calculations, instead of the HCOOH or CO products, the initial hydrogenation of CO₂ on SAAs would form the *CO intermediate, which could be further hydrogenated to produce methane. In addition, we have identified the bond angle of adsorbed *CO₂ can describe the CO₂ activation ability of TM₁/Cu (111) and the binding energy of *OH can describe the CO₂RR activity of TM₁/Cu (111). We speculated that the V/Cu (111) can show the best activity and selectivity for CO₂RR among all the 3d-TM-doped TM₁/Cu (111). This work could provide a rational guide to the design of new type of single-atom catalysts for efficient CO₂RR.

Green synthesis has grabbed appreciable attention to eliminate the negative effects associated with various chemical processes. Due to the unparalleled electrical, mechanical, thermal and excellent physical properties, graphene, as the thinnest two-dimensional material with high surface area, has the unfathomable potential in the domain of green chemistry in terms of both synthesis and application. In this regard, we present an overview of the research progresses on the greener synthesis of graphene, including micromechanical exfoliation, chemical reduction of graphene oxide (GO), chemical vapor synthesis and popping of GO. Meanwhile, various applications of graphene pertinent to sustainable developments, such as energy storage, catalysis, electrochemistry, fuel cell, supercapacitor and biomedicine have also been highlighted.