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.