Bipolar Plates (BPPs) play a critical role in Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) for effective hydrogen generation. The performance and longevity of the system can be considerably impacted by choosing the suitable material for these components. Polymer electrolyte membrane water electrolysis technology relies on cost-effective and corrosion-resistant BPPs. Tantalum, niobium, and titanium are low-cost, easy-to-machine materials that have good electrical and thermal conductivity; however, they exhibit low corrosion resistance. Noble metal and metal nitride coatings are usually investigated to minimize corrosion and interfacial contact resistance. Because of its performance-to-cost ratio, Stainless Steel (SS) based materials are among the most popular materials for BPP development. This study recommends material and operating parameters to improve PEMWE systems for sustainable hydrogen production’s efficiency, durability, and economic viability.

The advancement of catalytic materials is critical to improving the performance, reducing the cost and enhancing the sustainability of Proton Exchange Membrane (PEM) fuel cells and electrolyzers. Although Platinum Group Metal (PGM)-based electrocatalysts exhibit high electrochemical activity, their limited availability and the environmentally intensive extraction pose significant challenges. This study aims to demonstrate the direct reuse of recycled impure platinum (Pt) precursors for the synthesis of effective Pt/C electrocatalysts as a viable step toward circular hydrogen economy implementation. A low-cost and eco-friendly chlorine-based hydrometallurgical method was successfully employed to recycle over 99% of Pt from End-of-Life (EoL) Membrane Electrode Assemblies (MEAs), with an industrial perspective. Recycled metal precursor was used without purification to synthesize Pt/C electrocatalyst via a scalable and sustainable method. The catalyst was structurally and chemically characterized, and their electrochemical performance towards the Oxygen Reduction Reaction (ORR) was conducted under conditions simulating real operating environments. The recycled-metal-derived catalyst demonstrated comparable activity toward ORR (170 A/gPt) relative to a commercial catalyst, indicating its potential as viable alternative to conventional PGM-based catalysts. By integrating energy-efficient recycling with advanced material design, this work supports the development of cost-effective and green solutions for clean energy technologies aligned with a circular hydrogen economy model.

Platinum group metals (PGMs), platinum (Pt), palladium (Pd) and rhodium (Rh), are critical for automotive emission control, chemical manufacturing and emerging energy technologies, yet their supply is limited and geographically concentrated. Their designation as critical raw materials (CRMs) in the EU has intensified recycling efforts, especially from spent automotive catalysts. Conventional pyrometallurgical and acid-based hydrometallurgical routes achieve high recovery efficiencies but rely on aggressive reagents and energy-intensive processing. Deep eutectic solvents (DESs) have emerged as greener leaching media capable of dissolving PGMs under milder and tunable conditions. This review outlines the conventional hydrometallurgical framework, summarizes DES fundamentals relevant to metals dissolution, and critically assesses recent advances in DES-based leaching of PGMs from spent catalysts. The influence of solvent composition, oxidants and complexing ligands on PGMs speciation and recovery is discussed, together with emerging reporting guidelines and research priorities. Overall, DES-based leaching offers a promising and potentially safer route for autocatalyst recycling but the technology remains at an early stage of development, requiring further mechanistic insight and sustainability evaluation.

Diesel-engine Heavy-Duty Vehicle (HDV) exhaust gas mixture contains pollutants including unburned hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matter. A catalyst-based emission control system is commonly used to eliminate the above pollutants. However, the excess of oxygen that exists in the exhaust gasses of diesel engines hinders the efficient and selective reduction of nitrogen oxides over conventional catalytic converters. The AdBlue^® solution, which is currently used to eliminate nitrogen oxides, is based on ammonia. The latter is toxic in high concentrations. The aim of this work is to develop an Oxygen Reduction System (ORS) to remove oxygen from the exhaust gas of diesel engines, allowing the successful catalytic reduction of nitrogen oxides on a reduction catalyst without the need for ammonia. The ORS device consists of dense composite dual-phase membranes that allow the permeation of oxygen and carbon dioxide. Even though the oxygen concentration gradient across the membranes favors oxygen spontaneous diffusion from the atmosphere to the exhaust gas, the carbonate ion-based technology proposed herein utilizes the big difference in the concentration of carbon dioxide across the membrane to remove oxygen without any power consumption requirement. The results of this study are promising for the application of O₂ reduction in diesel HDVs.

The rapid expansion of hydrogen technologies has intensified the demand for platinum group metals (PGMs), particularly platinum (Pt) and iridium (Ir). Proton exchange membrane fuel cells (PEMFCs) and proton exchange membrane water electrolyzers (PEMWEs) rely on PGMs and fluoropolymer membranes such as Nafion, generating increasing volumes of end-of-life (EoL) membrane electrode assemblies (MEAs). Conventional recycling routes are often energy-intensive, hazardous and limited in polymer recovery. In this study, a closed-loop hydrometallurgical recycling route is assessed through a life cycle assessment (LCA), supported by primary experimental data from optimized recycling trials. Mechanical delamination enabled separation of catalyst layers while preserving membranes, followed by a chlorine-based hydrometallurgical process operating under mild conditions. Leaching efficiencies exceeded 99% for Pt and 80% for Ir, demonstrating the feasibility of metal recovery. Two LCA models were developed: (i) a gate-to-gate recycling model for EoL MEAs and (ii) a cradle-to-gate manufacturing model comparing virgin and recycled Pt. Results showed that substituting virgin Pt with recycled Pt reduced the global warming potential of MEA manufacturing by up to 70%. The analysis also identified electricity demand and Nafion membrane waste as key environmental hotspots. Overall, the study highlights the potential of closed-loop recycling to enhance circularity in hydrogen technologies.