Proton Conductivity in Solid Acid Fuel Cells

Solid acid fuel cells harness proton conduction through crystalline acid salts, most notably cesium dihydrogen phosphate (CsH₂PO₄) and related compounds, at intermediate temperatures (150–300 °C). Below a critical superprotonic phase transition, proton mobility is modest and governed by hydrogen‐bond dynamics; above this transition, a dramatic reorganisation of the hydrogen‐bond network triggers a jump in conductivity to values exceeding 10⁻² S cm⁻¹. The combination of high proton conductivity, chemical stability under humidified conditions and relatively low operating temperature makes solid acids promising electrolytes for compact, efficient power sources and electrochemical hydrogen pumps. Key challenges include controlling dehydration under dry atmospheres, tailoring microstructure to minimise resistive grain boundaries and integrating composite membranes for mechanical robustness. Recent advances have resolved conduction mechanisms at the atomic scale, optimised processing routes to yield sub‐micrometre electrolyte particles and explored composite architectures that stabilise conductivity over broader thermal and humidity regimes. This convergence of materials chemistry, processing technology and device engineering underpins the global drive towards zero‐emission energy conversion and decentralised hydrogen technologies.

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Proton Conductivity in Solid Acid Fuel Cells publication trend

The graph below shows the total number of articles in proton conductivity in solid acid fuel cells across all publications each year (not limited to Nature Index journals).

Technical terms

Proton conductivity: Measure of a material’s ability to transport protons under an electric field.

Superprotonic phase transition: A structural change in solid acids that causes a sudden increase in proton mobility.

Solid acid electrolyte: Crystalline acid salt that conducts protons, used as ion‐conducting separator in fuel cells.

Grain boundary: Interface between adjacent crystallites whose structure can impede or facilitate proton transport.

Metal–organic framework (MOF): Porous crystalline network formed from metal nodes and organic linkers, used here to enhance electrolyte dispersion and stability.

Cold sintering: Low‐temperature densification technique for ceramics employing transient liquid phases under pressure.

References

1. Alternative processing routes on CsH2PO4 proton conductors: Cold sintering and ball-milling routes. International Journal of Hydrogen Energy (2024).
2. SnO 2 modified CsH 2 PO 4 (CDP) protonic electrolyte for an electrochemical hydrogen pump. Energy Advances (2025).
3. New Type of Nanocomposite CsH2PO4-UiO-66 Electrolyte with High Proton Conductivity. Molecules (2022).
4. Facile and scalable synthesis of sub-micrometer electrolyte particles for solid acid fuel cells. RSC Advances (2018).
5. Characterization of the Dynamics in the Protonic Conductor CsH2PO4 by 17O Solid-State NMR Spectroscopy and First-Principles Calculations: Correlating Phosphate and Protonic Motion. Journal of the American Chemical Society (2015).