Harnessing Electrocatalytic CO2 Conversion to Produce Sustainable Aviation Fuels from Industrial Emissions

The Urgency of Decarbonizing Aviation

The aviation industry accounts for approximately 2-3% of global CO₂ emissions, with projections indicating this share could triple by 2050 without intervention. While electrification works for ground transportation, the energy density requirements of aircraft make sustainable liquid fuels the most viable near-to-medium term solution for decarbonizing aviation.

Electrocatalytic CO2 Conversion Fundamentals

Electrocatalytic CO₂ reduction (eCO₂R) utilizes renewable electricity to drive chemical reactions that convert CO₂ into valuable hydrocarbons. The process occurs at the interface between an electrocatalyst and electrolyte solution, where CO₂ molecules undergo multi-step reduction:

• CO₂ adsorption onto catalyst active sites
• Initial reduction to *CO intermediate (rate-limiting step)
• C-C coupling to form C₂₊ products
• Hydrogenation to form final hydrocarbon products

Theoretical Considerations

The thermodynamics favor different products based on applied potential:

• Formate (HCOOH) at -0.61V vs. RHE
• Carbon monoxide (CO) at -0.53V vs. RHE
• Methane (CH₄) at -0.48V vs. RHE
• Ethylene (C₂H₄) at -0.34V vs. RHE

Catalyst Development for Jet Fuel Precursors

The key challenge lies in selectively producing C₈-C₁₆ hydrocarbons suitable for aviation fuel. Current research focuses on several catalyst families:

Copper-Based Catalysts

Copper uniquely produces multi-carbon products, but suffers from poor selectivity. Recent advances include:

• Oxide-derived copper with enhanced *CO binding energy
• Copper-alloy systems (Cu-Ag, Cu-Sn) that modify intermediate adsorption
• Morphology-controlled nanostructures (nanocubes, nanowires)

Molecular Catalysts

Organometallic complexes offer precise control over reaction pathways:

• Cobalt phthalocyanines for selective CO production
• Iron porphyrins with proton relays for methanol formation
• Tandem systems combining molecular and heterogeneous catalysts

Emerging Materials

• Single-atom catalysts: Maximizing atom efficiency while maintaining selectivity
• Metal-organic frameworks: Tunable pore environments for controlled C-C coupling
• Bimetallic systems: Combining CO-producing and C-C coupling functions

Reactor Engineering Challenges

The transition from laboratory-scale demonstrations to industrial implementation requires addressing several engineering challenges:

Mass Transport Limitations

The low solubility of CO₂ in aqueous electrolytes (~34 mM at 25°C) creates mass transport bottlenecks. Solutions under investigation include:

• Gas diffusion electrodes (GDEs) with three-phase boundaries
• Microfluidic reactor designs with enhanced gas-liquid interfaces
• Pressurized systems to increase CO₂ concentration at catalyst sites

Product Separation and Recovery

The complex product mixtures require efficient separation strategies:

• In-line gas-liquid separators for volatile products
• Electrodialysis for organic acid recovery
• Cascade systems combining multiple reactor stages

System Integration Considerations

• Renewable energy matching: Dealing with intermittent power supply
• Heat management: Exothermic reactions require thermal control
• Scale-up factors: Maintaining performance at increased current densities (>200 mA/cm²)

The Full Value Chain: From CO₂ to Jet Fuel

A complete sustainable aviation fuel (SAF) production system involves multiple steps beyond the electrochemical conversion:

Economic and Environmental Considerations

Cost Breakdown Analysis

The levelized cost of e-fuel production depends on several factors:

• Electricity: Needs to be <$30/MWh to compete with fossil jet fuel at $3/gallon
• Capital costs: Electrolyzer stacks account for ~40% of system cost currently
• Catalyst lifetime: Targets >20,000 hours for commercial viability

Life Cycle Assessment Parameters

• Cradle-to-grave emissions: Potential for >70% reduction compared to fossil jet fuel when using renewable electricity and DAC-sourced CO₂
• Water usage: Approximately 1-1.5 kg water per kg fuel produced
• Land footprint: Significantly lower than biomass-based SAF pathways

The Path Forward: Research Priorities and Challenges

Key Performance Targets (2030 Horizon)

• C₄₊ Faradaic efficiency:>60% at >200 mA/cm²
• Cathode stability:>10,000 hours with <10% performance degradation
• Coupled system efficiency:>50% (electricity to liquid fuel)
• Capex reduction:<$500/kW for complete systems

Crucial Knowledge Gaps Requiring Investigation

• The mechanism of C-C coupling beyond C₂
• The role of electrolyte composition in product distribution
• The impact of impurities (SO_x, NO_x) from industrial flue gas feeds on catalyst performance and lifetime