Electrochemical reduction of CO₂ on graphene supported transition metals – towards single atom catalysts

Abstract

In this study, we have investigated the use of single metal atoms supported on defective graphene as catalysts for the electrochemical reduction of CO using the first-principles approach and the computational hydrogen electrode model. Reaction pathways to produce a variety of C products CO, HCOOH, HCHO, CHOH and CH have been studied in detail for five representative transition metals Ag, Cu, Pd, Pt, and Co. Different pathways were revealed in contrast to those found for metallic crystalline surfaces and nanoparticles. These single atom catalysts have demonstrated a general improvement in rate limiting potentials to generate C hydrocarbons. They also show distinct differences in terms of their efficiency and selectivity in CO reduction, which can be correlated with their elemental properties as a function of their group number in the periodic table. Six best candidates for CH production are identified by conducting computational screening of 28 d-block transition metals. Ag has the lowest overpotential (0.73 V), and is followed by Zn, Ni, Pd, Pt and Ru with overpotentials all below 1 V. Cu in the supported single atom form shows a strong preference towards producing CHOH with an overpotential of 0.68 V well below the value of 1.04 V for producing CH.

Electrochemical CO2 Reduction to C1 Products on Single Nickel/Cobalt/Iron‐Doped Graphitic Carbon Nitride: A DFT Study

“…All elementary steps with their free‐energy changes are presented in Table S4 (in the Supporting Information). The free energies of the initial protonation steps for CRR (*CO 2 +H + +e − →*COOH or *CO 2 +H + +e − →*OCHO) and HER (proton–electron pair, H + +e − ) can be calculated to discern the selectivity for CRR and HER . Figure shows the selectivity for CRR versus HER on Ni‐C 3 N 4 , Co‐C 3 N 4 , and Fe‐C 3 N 4 , in which the part below the dashed line are CRR‐selective catalysts.…”

“…*OCHO) and HER (proton-electron pair,H + + e À )c an be calculated to discern the selectivity for CRR and HER. [19,20,41,42] Figure 5s hows the selectivity for CRR versusH ER on Ni-C 3 N 4 ,C o-C 3 N 4 ,a nd Fe-C 3 N 4 ,inwhich the part below the dashedline are CRR-selective catalysts. Ther esults show that Ni-C 3 N 4 ,C o-C 3 N 4 ,a nd Fe-C 3 N 4 are CRRs electivew ith only one favorable initial protonation step.…”

Single Atoms on Graphene for Energy Storage and Conversion

“…To further validate the competitive relationship between the CO 2 RR and HER, theoretical analyses of CO 2 RR and CO desorption barriers are also performed to compressively understand the catalytic mechanism in electrochemical process . According to the DFT simulations, the electrocatalytic activities and selectivity of CO 2 depends on the kinds of catalysts (such as noble or transition metal catalysts).…”

Recent Progress in the Theoretical Investigation of Electrocatalytic Reduction of CO2

“…The Be-loaded BN [156] and Cu/Mo doped g-C 3 N 4 [157] have been studied theoretically, showing synergistic effect of both metal and the heteroatoms. [160] Beyond the single metal atom catalytic reaction, Sun's group studied the metal dimers supported by graphene derivatives as the active sites for CO2RR. [158] They predicted that both copper and nearby nitrogen were active sites which could connect with the key intermediates, as displayed in Figure 17b.…”

“…Based on similar systems, He et al reported that Ag-and Cu-doped graphene was a potential electrocatalyst for CO2RR to methane and methanol respectively. [160] Beyond the single metal atom catalytic reaction, Sun's group studied the metal dimers supported by graphene derivatives as the active sites for CO2RR. [161,162] Using large-scale screening-based DFT and microkinetics modeling, Cu 2 , CuMn, and CuNi dimers supported on graphene with adjacent vacancies were identified as improved electrocatalysts for CO, CH 4 , and CH 3 OH productions, respectively.…”