(390g) Investigation of Proton-Intercalating Electrode Materials for Energy-Efficient Aqueous Electrochemical Carbon Dioxide Capture

Electrochemically-mediated CO₂ capture (EMCC) represents a promising alternative to traditional thermal or pressure-driven CO₂ capture processes, potentially benefiting from lower theoretical energy requirements and facile integration with renewable, low-carbon energy sources. However, many proposed EMCC processes are currently limited by the cost and chemical instability of redox-active CO₂ sorbents, or rely on energy-intensive electrolysis/water dissociation processes. Recently, an alternative EMCC process was proposed that utilizes cyclic (de)intercalation of protons in manganese dioxide (MnO₂) electrodes to drive large pH-swings in an aqueous alkali-carbonate electrolyte, enabling pH-driven aqueous CO₂ capture without requiring conventional electrolysis, precious-metal catalysts, or specialized membranes. While this approach exhibits promising energy efficiency advantages, previous bench-scale demonstrations of this MnO₂ process were limited to low operational current densities. Thus, we sought to gain fundamental insight into stability and mass transport limitations of this system to inform the design of electrode materials with improved proton-coupled electron transfer (PCET) kinetics, proton transport rates, and electrochemical stability.

Detailed characterization work allowed us to gain further insight into the oxidation state and local coordination environment of the manganese oxide system, clarifying the role of morphology, oxidation state, and crystal structure on the PCET activity and electrochemical stability of MnO₂. This knowledge was then leveraged to extend the approach of heterogeneous PCET mediators for CO₂ capture to other metal oxide systems, correlating their structural properties with electrochemical and CO₂ capture performance. We also explored the addition of conductive polymers and ionomers to these metal oxide systems, which we hypothesized could increase proton transport and storage in these materials. Overall, this work aims to explore the use of metal oxide and polymer-based materials with enhanced stability and proton transport rates for use in electrochemical CO₂ capture, as well as potential synergies of these materials in the form of polymer metal-oxide nanocomposites.