Phosphorus-Doped Graphene Aerogel as Self-Supported Electrocatalyst for CO2 -to-Ethanol Conversion

Abstract

Electrochemical reduction of carbon dioxide (CO₂ ) to ethanol is a promising strategy for global warming mitigation and resource utilization. However, due to the intricacy of C─C coupling and multiple proton-electron transfers, CO₂ -to-ethanol conversion remains a great challenge with low activity and selectivity. Herein, it is reported a P-doped graphene aerogel as a self-supporting electrocatalyst for CO₂ reduction to ethanol. High ethanol Faradaic efficiency (FE) of 48.7% and long stability of 70 h are achieved at -0.8 V_RHE . Meanwhile, an outstanding ethanol yield of 14.62 µmol h^-1 cm^-2 can be obtained, outperforming most reported electrocatalysts. In situ Raman spectra indicate the important role of adsorbed *CO intermediates in CO₂ -to-ethanol conversion. Furthermore, the possible active sites and optimal pathway for ethanol formation are revealed by density functional theory calculations. The graphene zigzag edges with P doping enhance the adsorption of *CO intermediate and increase the coverage of *CO on the catalyst surface, which facilitates the *CO dimerization and boosts the EtOH formation. In addition, the hierarchical pore structure of P-doped graphene aerogels exposes abundant active sites and facilitates mass/charge transfer. This work provides inventive insight into designing metal-free catalysts for liquid products from CO₂ electroreduction.

Keywords: CO2 reduction; electrocatalysis; ethanol; graphene aerogel; phosphorus.

Figure 1

a) Schematic illustration of the synthesis process. b) SEM image, c) TEM image (inset HR‐TEM image), and d) EDS mapping of PGA‐2. e) XRD patterns and f) high‐resolution XPS spectra of P 2p for all samples.

Figure 2

a) LSV curves tested in CO₂‐saturated 0.5 M KHCO₃ solution for all samples. FEs of all products at different potentials on b) PGA‐1, c) PGA‐2, and d) PGA‐3. e) Comparison of EtOH yield with different catalysts. f) Stability test on PGA‐2. g) LSV curves of PGA‐2 tested in H‐cell and flow cell. h) EtOH FE and yield on PGA‐2 in flow cell.

Figure 3

a) Potential‐dependent and b) time‐dependent in situ Raman spectra in CO₂‐saturated 0.5 m KHCO₃ solution on PGA‐2.

Figure 4

The top and side view of local charge density difference between *CO and basic slabs a) P₁@ZZG and b) P₂@ZZG (the left figure is without the iso‐surface and the right is with iso‐surface. Yellow and teal represent the accumulation and depletion of electrons. Isovalue = 0.001; color code: P, purple; H, white; O, red; C, brown). c) Free energy diagram of three possible reaction pathways for CO₂ reduction to EtOH on P₂@ZZG at U = 0 V.