Nature Communications · 2025
Gravity-Assisted Product Self-Separation (GAPS) Reactor
A breakthrough in electrochemical oxygen removal that leverages Stokes flow and buoyancy-driven bubble dynamics to achieve 95% product self-separation — eliminating the need for costly ion-exchange membranes.
Original Publication
Li, P., Tang, X., Zhou, X., et al. "A membrane-free electrochemical reactor for efficient oxygen removal via gravity-assisted product self-separation."
Nature Communications, 16, 4309 (2025). DOI: 10.1038/s41467-025-59506-7
University of Science and Technology of China · Hefei Hualing Co., Ltd · Anhui Entropy Carnot Energy Technology Co., Ltd
Performance Metrics
Product Self-Separation
95%
O₂ bubbles self-separate via buoyancy without membranes
Operational Lifespan
10 years
Integrative GDE with 30× greater stability than carbon paper
Fresh-Keeping Improvement
3.4×
Two-cell system in household refrigerator
Cost Efficiency
22.6×
O₂ removal per unit cost vs. ion-exchange membrane reactors
The Science
The GAPS Reactor exploits the density differences among three phases — the electrode (high density), the liquid electrolyte (medium density), and the gas phase (low density) — to achieve spontaneous, buoyancy-driven O₂ migration.
When O₂ bubbles form at the anode through the oxygen evolution reaction (OER), they immediately enter the bulk electrolyte. The inherent density gradient creates a self-organizing "O₂ ladder" that allows bubbles to naturally ascend and exit the liquid surface without external pumping or membrane separation.
The cathode, positioned at the reactor's base, performs the oxygen reduction reaction (ORR), selectively removing O₂ from the storage environment. A large-area open cathode design overcomes mass transfer limitations that would otherwise result from the absence of a gas-liquid circulation system.
Stokes Flow — Reynolds Number
Where ρ_l is liquid density, v_b is bubble rising speed, 2r is bubble diameter, and μ_l is liquid viscosity.
Bubble Terminal Velocity
Using 20% K₂CO₃ electrolyte: v_b = 0.175–0.486 m/s for r = 0.3–0.5 mm. Bubble rise time for h = 0.05 m is 0.10–0.28 s.
Electrochemical Reactions
Engineering Innovation
Conductivity
85.5%
relative to conventional carbon paper
Gas Permeability
80.2%
relative to conventional carbon paper
Mechanical Strength
2.2×
higher than carbon paper GDE
The integrative GDE addresses the critical limitations of traditional carbon paper-based electrodes. By thoroughly mixing carbon spheres with a high loading of PTFE and sintering the mixture, the resulting electrode achieves uniform PTFE distribution — eliminating the uneven distribution that undermines the electrochemical stability of conventional designs. The result is an electrode with 30× greater operational stability, enabling the 10-year lifespan required for consumer applications.