Power-to-X with biological step

01Overview and value chain

Markers: [EC: REACH / Renewable Energy Directive III | OECD: bioenergy | Regulator: EPA (USA), REACH (EU), NEA (China)]

Power-to-X with a biological step uses renewable electricity to drive living microbes that reduce CO2 into fuels, chemicals and protein. The flagship mode, microbial electrosynthesis (MES), runs at a cathode immersed in an anaerobic broth of electroactive acetogens such as Sporomusa ovata or Clostridium ljungdahlii: electrons travel from the electrode into the cell — directly through outer-membrane cytochromes and conductive nanowires, or indirectly via electrolytically generated hydrogen — and the microbe uses them, together with CO2, to build acetyl-CoA through the Wood-Ljungdahl pathway. From that central intermediate it releases acetate, ethanol or butanol, or grows as single-cell protein. A closely related mode, power-to-methane, uses hydrogenotrophic archaea such as Methanothermobacter to convert CO2 and green hydrogen into grid-quality biomethane. Unlike abiotic Power-to-Gas (water electrolysis plus a high-temperature Sabatier reactor), the biological route runs at ambient pressure and around 30-37C, which is its main engineering appeal and its main scale-up hurdle.

The key directions of power-to-X with a biological step are:

1. Microbial electrosynthesis to acetate and chemicals (MES to Acetate & Chemicals): electroactive acetogens at a cathode fix CO2 into C2-C6 building blocks (acetate, ethanol, butanol) for the green-chemistry and polymer industries.
2. Power-to-methane / biological methanation (Power-to-Methane): hydrogenotrophic archaea convert CO2 and green hydrogen into pipeline-quality biomethane for gas-grid injection.
3. CO2-to-protein (CO2-to-Protein): hydrogen-oxidizing microbes turn electricity-derived hydrogen and CO2 into single-cell protein for feed and food.
4. Electrode and biofilm engineering (Electrode & Biofilm Engineering): high-surface-area 3D porous cathodes and conductive biofilms raise the electron-transfer rate that ultimately sets reactor productivity.

Sectoral value chain

[renewable power + CO2] ──> [MES bioelectrochemical reactor] ──> [cathode electron transfer to microbes]
                                                                                    │
                                                                      (Wood-Ljungdahl CO2 fixation)
                                                                                    │
            [target product: acetate / methane / protein] <─── [membrane separation] <─── [metabolite-rich broth]

Value chain levels

Cross-cutting technologies of the sector:

• Cathode-to-microbe electron transfer (Electron Transfer Interface): direct transfer via cytochromes and conductive pili, plus H2-mediated transfer via hydrogenases, together set the coulombic efficiency of the cell.
• Wood-Ljungdahl pathway (Wood-Ljungdahl Pathway): the most energy-efficient biological CO2-fixation route, converting two CO2 molecules into one acetyl-CoA that branches into acetate, alcohols and biomass.
• Pressurized gas dissolution (Hollow-Fiber Membrane Biofilm Reactors): hollow-fiber membranes deliver CO2 and hydrogen bubble-free straight into the biofilm, lifting gas availability into the cells.

02US

The US funds microbial electrosynthesis through the Department of Energy and the national labs, while a cluster of startups pushes CO2-to-chemicals and CO2-to-protein routes toward commercial scale.

DOE and NREL R&D, CO2-to-chemicals startups, gas-fermentation anchor

• DOE Office of Science and NREL: federal grants fund the electrode-cell interface and acetogen metabolic engineering; NREL develops scalable bioelectrochemical reactors with high-area cathodes.
• Cemvita Factory: uses engineered Wood-Ljungdahl microbes to make bio-ethylene, glycols and other olefins straight from CO2 and electricity, targeting electrofuels and bio-based plastics.
• NovoNutrients: runs hydrogen-driven gas fermentation to turn CO2 and electricity-derived hydrogen into single-cell-protein ingredients for aquafeed and food.
• LanzaTech (commercial anchor): although gas-fermentation rather than electrosynthesis proper, its commercial CO/CO2-to-ethanol plants are the reference deployment that MES routes aim to displace on cost.

03CN

China couples surplus wind and solar in its western provinces to bioelectrochemical and biomethanation pilots, backed by CAS institutes and the National Energy Administration’s decarbonization mandate.

CAS Shenzhen MES R&D, western-province power-to-gas, industrial-biotech scale-up

• CAS Shenzhen Institute of Advanced Technology: a leading Chinese MES R&D center, engineering conductive-polymer biofilms and carbon-nanotube composite cathodes to raise coulombic efficiency.
• Western-province integration: curtailed wind and solar in Xinjiang and Gansu power bioelectrochemical reactors that convert CO2 from coal-plant flue gas into stable biomethane for the West-East gas pipeline.
• Dalian Institute of Industrial Biotechnology (CAS): scales one-carbon gas-fermentation and bioelectrochemical processes from bench to industrial demonstration, anchoring the Chinese industrial-biotech pipeline.

04EU

The EU leads on commercial biological methanation and funds multi-center MES consortia under Horizon Europe, framed by REACH and the Renewable Energy Directive.

Electrochaea commercial biomethanation, Horizon Europe Power-to-X, academic MES hubs

• Electrochaea: operates commercial-scale biological methanation plants in Denmark and Switzerland; its patented thermophilic Methanothermobacter catalyst converts CO2 and green hydrogen into pipeline-quality biomethane at high selectivity.
• Horizon Europe Power-to-X programs: targeted funding integrates Power-to-X with wastewater and biogas plants, using their CO2 streams as feedstock.
• Academic MES hubs: the University of Girona and Ghent University advance MES reactor design — 3D porous carbon cathodes and biofilm engineering — for specialty acids from industrial emissions.

05Leading companies and research institutes

06Tech stack and innovations

The stack sits at the intersection of electrocatalysis, strict-anaerobe physiology and high-pressure gas mass transfer.

1. Cathode-to-microbe electron transfer (Electron Transfer Interface):
   • direct transfer: bacteria dock on the cathode through c-type cytochromes and conductive nanowires; 3D porous carbon-felt cathodes, often loaded with nickel or magnetite nanoparticles, enlarge the contact area.
   • H2-mediated transfer: the cathode electrolyzes water to hydrogen at mild overpotential (molybdenum-disulfide or low-platinum coatings), and bacterial hydrogenases split the hydrogen to feed reduction.
2. Wood-Ljungdahl pathway biochemistry (Wood-Ljungdahl Pathway):
   • the most energy-efficient CO2-fixation route: a methyl branch reduces one CO2 to a methyl group (via formate and tetrahydrofolate) while a carbonyl branch reduces a second CO2 to CO (via CODH); acetyl-CoA synthase condenses them into acetyl-CoA, which branches to acetate, alcohols and biomass.
3. Pressurized gas dissolution (Hollow-Fiber Membrane Biofilm Reactors):
   • hydrogen and CO2 are poorly soluble in water; hollow-fiber membrane biofilm reactors (HfMBR) deliver the gases bubble-free at mild pressure straight into the biofilm growing on the fiber outer wall, lifting gas availability into the cells.

07Value chains and production pipelines

Industrial pipeline of continuous microbial electrosynthesis of green acetic acid from renewable power and industrial CO2 (Sporomusa ovata biocathode, HfMBR reactor, membrane ultrafiltration, LIMS/EPD)

┌───────────────────────────┐      ┌───────────────────────────┐
│ 1. Electroactive biofilm  │ ───> │ 2. CO2 capture & feed to  │
│    growth on the cathode  │      │    the HfMBR electrolyser │
└───────────────────────────┘      └───────────────────────────┘
                                                 │
                                                 ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 4. Two-stage membrane     │ <─── │ 3. Microbial              │
│    ultrafiltration        │      │    electrosynthesis of    │
│                           │      │    acetate under current  │
└───────────────────────────┘      └───────────────────────────┘
              │
              ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 5. Acidification & vacuum │ ───> │ 6. Purity QC & LIMS/EPD   │
│    rectification to glacial│      │    carbon-footprint passport│
│    acetic acid            │      │                           │
└───────────────────────────┘      └───────────────────────────┘

Stage 1: Electroactive biofilm growth on the cathode

A pure culture of Sporomusa ovata is grown anaerobically and pumped into the bioelectrochemical reactor, whose cathode is a high-area 3D carbon felt. Under a mild cathode potential the bacteria colonize the felt over several days, forming a thin conductive biofilm that will accept electrons from the electrode.

Stage 2: CO2 capture and feed to the HfMBR electrolyser

Dry CO2 captured from cement- or steel-plant flue gas is compressed and fed into the hollow porous polypropylene fibers that thread the cell, while the IrO2-coated anode receives clean water. The reactor draws DC current from a neighbouring wind or solar farm.

Stage 3: Microbial electrosynthesis of acetate under current

At the anode, water oxidizes to oxygen and protons; the released electrons travel through the external circuit to the cathode, where the Sporomusa biofilm takes them up and reduces the CO2 diffusing in from the fibers. Via the Wood-Ljungdahl pathway the cells steadily release acetate into the broth; pH is held near neutral by alkali dosing and the sodium-acetate broth is drawn off continuously.

Stage 4: Two-stage membrane ultrafiltration

The broth passes through a two-stage membrane plant: ceramic ultrafiltration retains and recycles the cells back to the reactor, and nanofiltration separates acetate salts from the residual mineral salts of the medium.

Stage 5: Acidification and vacuum rectification

The concentrated sodium acetate is acidified to liberate free acetic acid and sent to a vacuum rectification column; running under reduced pressure drops the boiling point, avoiding thermal degradation and saving energy, and leaves glacial acetic acid in the reboiler.

Stage 6: Purity QC and LIMS/EPD carbon-footprint passport

Each batch is checked by GC-MS for acetic-acid titre and trace metals, and coulombic efficiency is logged. The LIMS system certifies the product against food and chemical specifications and issues an EPD carbon-footprint passport showing the reduction versus the petrochemical route, after which the green acid is shipped.