The core reaction at the cathode air electrode of alkaline fuel cells (AFCs) is the oxygen reduction reaction (ORR). Conventional binders such as PTFE and PVDF suffer from drawbacks including easy degradation in alkaline environments, pore blockage, and contamination. As a water-soluble cellulose ether, HPC can be utilized as an electrode binder and film-forming auxiliary, which is compatible with the high-concentration KOH strong alkaline system of AFCs and delivers multiple merits in electrochemistry, manufacturing process and environmental protection.

Chemical Stability in Strong Alkaline Systems (Core Advantage for AFC Matching)

1. Wide pH Alkali Resistance Compatibility

The hydroxypropyl side chains on HPC molecules shield the cellulose backbone, rendering a stable pH range of 2–11. HPC resists hydrolytic chain scission for long-term service in KOH electrolytes below 6 mol/L, the commonly adopted concentration for AFCs. In contrast, PVDF undergoes rapid dehydrofluorination and degradation in concentrated alkali, while PTFE becomes brittle and fails under high-temperature strong alkaline conditions. HPC maintains intact electrode frameworks over prolonged operation and extends cycle life by over 30%.

2. Salt-Induced Self-Curing with Pore-Locking Structure

Mild salting-out effect occurs upon contact with highly alkaline electrolytes, triggering slight crosslinking and curing of polymer chains to firmly immobilize carbon powder and ORR catalyst particles. No swelling-induced collapse or gas channel blockage takes place. Dual pathways for oxygen diffusion and OH⁻ conduction are preserved, mitigating the flooding issue of air electrodes.

3. Fluorine-Free with Zero Byproduct Contamination

Free of fluorine elements, HPC generates no HF or fluoride impurities during charge and discharge cycles, thereby preventing poisoning of precious-metal and non-precious-metal cathode catalysts in AFCs. It addresses the persistent catalytic activity decay plaguing conventional fluorinated binders under long-term operation.

Advantages of Microscale Pore Channels and Mass Transfer (Boosting ORR Kinetics)

1. Amphipathic Hierarchical Pores for Simultaneous Gas, Liquid and Ion Transport

Possessing both hydrophilic hydroxyl groups and hydrophobic propyl groups, HPC forms hierarchical porous films after film formation. Hydrophilic channels conduct OH⁻ ions and electrolytes, while hydrophobic pores transport oxygen, constructing three-phase reaction interfaces. Cathodic polarization resistance is drastically reduced, and peak power density is elevated accordingly.

2. No Blockage of Catalytic Active Sites

A low dosage of merely 2%–5% suffices for binder functionality, yielding thin, permeable films that never encapsulate catalyst particles. By comparison, PTFE readily agglomerates to cover active sites and suppress oxygen reduction kinetics.

3. Water Retention Buffering for Stabilized Three-Phase Interfaces

Hydroxyl groups endow HPC with water-locking capacity to sustain optimal internal electrode humidity, avoiding interrupted ion conduction caused by cathode dehydration in AFCs. It accommodates low-temperature and low-humidification operating conditions with a wider operational tolerance window.

Rheological and Forming Advantages of Electrode Slurries

1. Green Aqueous Fabrication Process

Only pure water serves as solvent, eliminating toxic NMP and other organic solvents. Zero VOC emissions are achieved during production, cutting costs for explosion-proof facilities and environmental waste treatment. It is compatible with full electrode manufacturing workflows including blade coating, spraying and calendering.

2. Shear-Thinning Rheology Ensuring Excellent Slurry Homogeneity

Aqueous HPC solutions behave as pseudoplastic fluids: viscosity declines under stirring and coating shear force, enabling uniform dispersion of carbon powder and catalysts without agglomeration. Viscosity recovers at rest to prevent sedimentation and phase separation of slurries, significantly improving batch-to-batch consistency of electrodes.

3. Low-Temperature Film Formation with Superior Mechanical Flexibility

Continuous coherent binder films form upon low-temperature drying below 100 °C, avoiding thermal damage to non-precious-metal catalysts. The flexible films buffer volume deformation during charge-discharge cycles, inhibiting electrode cracking and shedding of active materials, and enhancing mechanical durability of electrodes.

Environmental and Cost Advantages

1. Biodegradable Bio-Based Raw Material

Derived from natural cellulose, spent electrodes with HPC undergo mild degradation without persistent plastic pollution, complying with green manufacturing standards for energy storage devices.

2. Lower Raw Material Cost

Compared with PTFE and perfluorinated ionomers, the mass production price of HPC is only one-third that of fluorinated binders, substantially cutting material costs for AFC air electrodes.

Comprehensive Application Summary

For air electrodes of alkaline fuel cells, HPC acts as an eco-friendly superior alternative to traditional fluorinated binders. Supported by three core merits—alkali-resistant stability, amphipathic porous mass transfer, and easy aqueous processing—HPC optimizes the three-phase interface for oxygen reduction, lowers cathode internal resistance and extends battery cycle life. Its performance deficiencies only emerge under ultra-high temperature and ultra-concentrated strong alkali operating conditions, which can be offset via blending and modification treatments. HPC boasts broad application prospects in civil low-temperature alkaline fuel cells and portable energy storage AFCs.