Air-breathing polymer electrolyte fuel cells: A critical review of recent progress and future research needs

Air-breathing polymer electrolyte fuel cells (PEFCs) are a simplified alternative to conventional forced-convection PEFC systems, eliminating external air-supply devices to reduce system complexity, weight, and cost, and to minimise parasitic losses. Despite these advantages, their passive configuration poses critical challenges in oxygen mass transport, water management, thermal regulation, and environmental sensitivity. This study presents a comprehensive bibliometric and systematic review of air-breathing PEFC research published between 2000 and 2025. Using the Scopus database and a PRISMA-guided screening framework, 224 relevant documents were analysed through the Bibliometrix package in RStudio and VOSviewer to map publication trends, international collaborations, keyword evolution, and thematic research clusters. The results indicate irregular but sustained growth in research output, with an annual growth rate of 8.67%. Keyword co-occurrence analysis identified major research themes centred on water management, gas diffusion layer optimisation, flow-field design, numerical modelling, thermal diagnostics, and durability enhancement. Emerging niches include piezoelectric-assisted mass transport and advanced membrane materials for high-temperature and miniature systems. The findings highlight that future technological progress depends on improved mass-transport engineering, enhanced membrane stability, optimised passive flow architectures, and integrated stack-level thermal management. For researchers, the study clarifies the field's conceptual evolution and highlights the most critical research gaps. For industry stakeholders, it provides strategic insights into design priorities for compact, reliable hydrogen-powered systems suitable for portable, off-grid, and unmanned aerial vehicle applications.