Cu Catalysts with Boron Dopants Boost Methane Production Efficiency
Recently, Prof. ZENG Jie from Hefei National Research Center for Physical Sciences at the Microscale and University of Science and Technology of China (USTC), collaborating with Prof. XIA Chuan’s group from the University of Electronic Science and Technology of China and Researcher Xiao Jianping’s group from the Dalian Institute of Chemical Physics, designed an atomically dispersed Cu catalyst towards methane (CH4) production via rationally regulating the nearest coordination environment with boron (B) dopants. Their work was published in Nature Communications on June 8th.
CH4 possesses the largest heating value among hydrocarbons and is an important raw material for chemical production such as aromatic hydrocarbon. Electrocatalytic CO2 conversion (CO2RR) into CH4 offers an entrancing opportunity to both store renewable electric energy and utilize CO2 emissions. Typical competing processes of CH4 formation in CO2RR include dimerization of CO* into C2 products and desorption of CO* into gaseous CO product. Single-atom catalysts (SACs) with adjustable and isolated active sites have been applied to electrochemical catalysis for its potential in expelling C-C coupling in CO2RR. However, the performance of Cu-N4 materials in methane production is still unsatisfactory, specifically, manifesting selectivity to CO at a less cathodic potential and sluggish kinetics to CH4 at a more cathodic potential.
Based on this concern, the research team proposed a general way to design atomically dispersed Cu catalysts by rationally regulating the nearest coordination environment in Cu-N4. Partial substitution of nitrogen atoms with relatively weak electronegativity functionality, B, facilitates the adsorption of key intermediates and thus steer the CO2RR selectivity towards CH4.
The researchers first built a series of Cu-NxBy structures with different boron concentrations and performed density functional theory (DFT) calculations to evaluate the thermodynamic activity trend of CO2RR to CH4. Compared to pristine Cu-N4, the B dopants can effectively enhance the reactivity of Cu sites and the adsorption energies. Projected density of states (PDOS) of CHO* adsorbed on different Cu-NxBy sites indicate much stronger electronic interaction between CHO* and Cu-NxBy sites. Inspired by the theoretical predictions, the researchers then manipulated the nearest neighbor structure of isolated Cu sites with B dopant (BNC-Cu). Comprehensive analysis of X-ray absorption spectroscopy (XAS) data revealed that atomically dispersed Cu in BNC-Cu possessed the B-doped Cu-Nx structure (Cu-NxBy) mainly in the form of Cu-N2B2.
Results showed a huge boost in CH4 production using B-doped Cu catalyst, with BNC-Cu showing a high CH4 Faradaic efficiency (FE) of 73% and partial CH4 current density (jCH4) of -292 mA cm-2 at -1.46 V vs. RHE. The divergence in CO2RR performance between B-doped and undoped Cu sites validated the theoretical predictions, demonstrating that doping B into Cu-N4 structure serves as an effective way to enhance deep reduction activity in CO2RR.