Towards Durable, Selective Catalysts and Electrodes for the Electroreduction of CO₂ to Value-Added Chemicals and Fuels

Increasing atmospheric carbon dioxide (CO₂) levels and the associated rise in global temperatures are major global concerns. Annually, the world emits an extra 14.7 Gt of atmospheric CO₂.¹ Electricity production and transportation are large atmospheric CO₂ contributors (~70% of total emissions), and therefore scientists have developed renewable energies and fuel cells vehicles as a mitigation strategies.^2,3 Another widely-studied mitigation approach is the electrochemical reduction of CO₂ (ECO₂RR) to value-added chemicals and fuels such as carbon monoxide, formic acid, ethylene, ethanol, and acetate can be made, which can serve as chemical feedstock for a variety of chemical processes.⁴ The chemical produced from ECO₂RR depends on the electrocatalyst and operating conditions utilized.

ECO₂RR research revolves around four benchmarks when considering industrial feasibility: high product Faradaic efficiency (selectivity), high current density (activity), low overpotentials (high energy efficiency), and robust durability/stability. Product selectivity and system durability greatly affect economic feasibility (i.e. separation and maintenance costs). Many groups have successfully concentrated on catalyst selectivity and activity. State-of-the-art catalysts for ECO₂ electroreduction can produce CO and HCOOH at high selectivity (>80%). However, a majority of ECO₂RR durability studies show lifetimes of <20h despite technoeconomic analyses benchmarks suggesting system lifetimes of >3000h.⁵

This presentation will provide ways to assess the durability and stability of cathodes and the need to study the mechanisms by which they lose activity, so called degradation. After a brief summary of recent ECO₂RR durability studies and common degradation mechanisms, we will then focus on methods for accelerating durability testing. Accelerated durability and stress testing are very common in other, more established electrochemical fields (fuel cell, water electrolysis, chlor alkali electrolysis), and will become relevant when the ECO₂RR field as a whole reaches longer lifetimes (≥50 h). Next, we address the challenges associated with electrode durability in alkaline media, specifically binder compatibility, by proposing new ways of preparing the catalyst layer in the cathode. The binder plays a large role in controlling hydrophobicity as well as protecting and improving the stability of the catalyst. With these studies, we aim to increase electrode durability in our alkaline ECO₂RR flow cell.

Acknowledgement

We gratefully acknowledge financial support from Shell New Energies Research & Technology's Dense Energy Carriers Program, I2CNER and the SURGE Fellowship for UN.

References

1. IPCC, Climate Change 2014 Synthesis Report Summary for Policymakers, https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf)

2. Oerlemans, Science, 2005, 308(5722), 675-677

3. https://www.eia.gov Accessed 05/29/2017

4. Hori, Modern Aspects of Electrochemistry, 2008, 89-189

5. U.O. Nwabara, E.R. Cofell, S. Verma, E. Negro, P.J.A. Kenis, ChemSusChem, 2020