Fabrication of Cu-Single Atom Catalyst Supported on Unique 2D Graphdiyne Analogue-Based Porphyrin Metal Covalent Organic Frameworks for Carbon Dioxide Reduction Application
Authors: Masaud Zubair , Huang Hao , Eric-Roseng Lars , Wang Kaiying 
Published: February 2024

Excessive burning of fossil fuels for energy production has led to an exponential increase in CO2 concentrations in the atmosphere, which is the core of universal problems such as global warming and climate change. One of the new approaches to reducing CO2 emissions is to think of CO2 as a useful raw material and convert this compound into useful products. Moreover, electrocatalytic carbon dioxide reduction (eCO2R) can be conveniently utilized to establish a zero-emission carbon cycle and utilize this CO2 for energy-dense fuels and other chemical raw materials [1]. However, exploring novel catalysts is the ultimate need of the hour for an effective and efficient eCO2R.
Heterogeneous single-atom catalysts (SAC) containing isolated metal species on an atomic level are gaining the increasing attention of the scientific community owing to their high metal utilization sites and superior catalytic properties[2]. The SACs are put into the full effect of catalysis by scattering it over conductive support. Therefore, in this work, the copper SACs are supported over a unique porphyrin-based graphdiyne (SAC-PG) with a π-conjugated structure (Figure 1). Graphdiyne possesses two acetylenic linkages between the aromatic rings and is responsible for not only displaying exceptional electronic conductivity but when coupled with the metalloporphyrin network provides numerous active sites for catalysis[3]. This SAC-PG analogue is achieved by a Glaser-Hay coupling reaction on Cu foam or foil. Moreover, SEM analysis is performed in combination with SEM-EDX and elemental mapping to investigate the morphology of the fabricated catalyst (Figure 2). In addition, this unique copper-based SAC-PG is evaluated as a catalyst for eCO2R in a customized H-cell with 0.1M/0.5M KHCO3 as an electrolyte and Pt as a counter electrode. Nafion 117 proton exchange membrane is used for separation between the cathodic and anodic compartments while an Ag/AgCl (3M KCl) was used as a reference electrode. Under these eCO2R conditions, the copper SAC-PG catalyst displayed extremely high current densities (32 – 75 mA/cm2) over a range of voltages (1.0-1.2 V vs RHE) and acceptable faradaic efficiencies for the carbon products (with maximum FE over 60% in total for all carbon products).
In conclusion, a 2D metal covalent organic framework containing a repeating unit of Cu-porphyrin linked by butadiyne linkages was established. This unique structure showed effective CO2R catalysis due to its nanoporous structure, high electronic conductivity, and abundant metal cites utilization. Further optimization and constriction of these easily adjustable catalysts open up various possibilities of further exploration in the field of eCO2R.

Acknowledgement: The author Zubair Masaud acknowledges support from the Norwegian Micro- and Nano-Fabrication Facility (NorFab, No. 245963/F50) The author Hao Huang acknowledges Marie Skłodowska-Curie Actions individual fellowship CarbonChem 101024758.

References

[1] I. Ganesh, “Electrochemical conversion of carbon dioxide into renewable fuel chemicals - The role of nanomaterials and the commercialization,” Renew. Sustain. Energy Rev., vol. 59, pp. 1269–1297, 2016, doi: 10.1016/j.rser.2016.01.026.
[2] X. Yang, A. Wang, B. Qiao, and J. U. N. Li, “Single-Atom Catalysts : A New Frontier,” vol. 46, no. 8, 2013.
[3] C. Huang et al., “Progress in Research into 2D Graphdiyne-Based Materials,” Chem. Rev., vol. 118, no. 16, pp. 7744–7803, 2018, doi: 10.1021/acs.chemrev.8b00288.

Figure 1