Plasma-deposited nano-carbon coatings for enhanced performance in PEM metal bipolar plates

Proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) face durability and cost challenges, with metallic bipolar plates (BPPs) susceptible to corrosion in acidic PEM environments. While amorphous carbon (a-C) coatings offer high conductivity and chemical inertness via tunable sp 2 /sp 3 hybridization, their long-term stability under harsh electrochemical conditions remains a concern. This review systematically examines recent advances in surface and interfacial engineering of carbon coatings for BPPs, integrating colloid and interface science with energy technology. It critically analyzes deposition techniques including magnetron sputtering, filtered cathodic vacuum arc, and plasma-enhanced chemical vapor deposition, focusing on plasma-surface interactions and defect control. Performance evaluation progresses from undoped and hydrogenated carbon coatings to single-element and multi-element doping, and finally to multilayer structures, detailing design principles, fabrication strategies, enhancement mechanisms, and degradation pathways. The review particularly emphasizes operando degradation studies, distinguishes degradation pathways between PEMFCs and PEMWEs, and discusses mitigation strategies for compressive stress-induced buckling. A quantitative comparison of deposition techniques is provided, including energy use, CO₂ footprint, and roll-to-roll manufacturing cost–benefit analysis. Critical commentary on the lack of standardized corrosion testing protocols is included. Industrial perspectives on scaling high-throughput deposition to meet U.S. DOE 2030 targets (ICR < 3 mΩ·cm 2 , cost < $5/kW) are discussed.