Selective CO2 Reduction to CO and Alcohols without Platinum or Noble Group Electrodes

Project Information

RECALLCO2

Grant agreement ID: 101117270

DOI

10.3030/101117270

EC signature date 3 November 2023

Start date 1 December 2023

End date 30 November 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 500 000,00

EU contribution

€ 1 500 000,00

Coordinated by

TECHNISCHE UNIVERSITEIT DELFT
Netherlands

Periodic Reporting for period 1 - RECALLCO2 (Selective CO2 Reduction to CO and Alcohols without Platinum or Noble Group Electrodes)

Reporting period: 2023-12-01 to 2026-05-31

Summary of the context and overall objectives of the project

The electrochemical conversion of CO2 to carbon-based feedstocks represents one of few technological routes capable of replacing fossil fuel derivatives. Despite substantial advancements, however, major challenges impair CO2 electrolysis from matching its promise. Critically, steady acidification of CO2 electrolyzers during operation currently necessitates the use of iridium-based anodes, an expensive and limited electrode material. More fundamentally, while CO2 reduction to CO, formate and ethylene has become highly selective, the production of high-energy density alcohols with high selectivity has been elusive. To overcome these barriers, new scientific approaches are needed.

RECALLCO2 aims to resolve iridium dependencies and non-selective alcohol production in CO2 electrolysis through a combination of novel electrochemical cell design and the development of molecular catalytic architectures which break existing limitations. To limit iridium dependencies bipolar membranes will be used as they allow for asymmetric pH conditions on either side of an electrolyzer. Maintaining these asymmetric conditions over long operating times is challenged by membrane crossover of other ion species. The project seeks to understand and limit crossover to meet its objectives.

A second pillar is the conceptualization that strong coupling of metal complexes to supports can enable the selective production of high-value alcohol products from CO2 with minimal competing reactions. While ethanol can be produced on copper catalysts, it is a minor product and requires multi-product valorization to be justified. Here we aim to delink electron transfers from a molecular catalyst’s oxidation states, and fundamentally change catalytic behavior that currently restricts reactions to 2 electrons. Thus, CO2 reduction products such as methanol (6 electrons) and ethanol (12 electrons) are targeted. A challenge and aim of the project is to push the use of molecular catalyst to membrane electrode cell assemblies, which is an essential step in minimizing cell voltages and scaling-up the technology.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first 24 months, the RECALLCO2 project has made strong progress toward its main objectives while establishing the experimental foundations needed for long-term impact. This initial phase focused on training early-career researchers and building reliable experimental platforms for testing new electrochemical concepts and materials.

A central achievement has been the investigation of electrochemical CO2 conversion using membrane-based systems. We identified how operating conditions such as current density and electrolyte composition control ion transport across the membrane, which in turn affects water dissociation efficiency and material stability. Crucially, we demonstrated stable CO2 electrolysis for over 150 hours using nickel-based components, highlighting the necessary steps and tradeoffs to using non-precious metal anodes.

In further work we showed how crossover could be decreased to <2% by maximizing current density and minimizing anolyte concentrations. These efforts have also identified a strong inverse trade-off between CO2 electrolysis activity and membrane crossover, which must be carefully controlled to maintain the desired cathodic reaction combined with anode stability. The work concluded by outlining a plan for an elevated water dissociation efficiency of ~99%, combined with reasonable electrolyte volumes and periodic bipolar membrane electrodialysis to recover alkaline conditions, and thus utilize nickel anodes instead of iridium.

The project has also addressed fundamental energy limits of electrochemical reactions relevant to sustainable chemistry, including CO2 conversion, nitrate removal, and seawater electrolysis. We clarify how asymmetric operating conditions influence voltage requirements for aqueous-based systems, and a publication is currently in preparation.

In parallel, new methods were developed to study how molecular catalysts interact with their supporting materials. These advances allow active catalytic sites to be distinguished from inactive species, improving efficiency and reproducibility. Finally, new catalyst deposition strategies led to proof-of-concept CO and methanol production from CO2 using carbon-based nanomaterials, providing a strong foundation for the next phase of the project.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the first stage of RECALLCO2 we advance the understanding ion crossover in bipolar membrane during CO2 electrolysis to valuable products. The results provide a criteria for membrane design to operate CO2 electrolyzers with non-platinum group materials. The work also unveiled the electrolyte asymmetry which is present in a large amount of water-based electrochemical processes. If left unaddressed, asymmetry in electrochemical systems limit the efficiencies which can be achieved, which will subsequently inhibit future appetites for demonstration scales and access to financial capital.