A model for the cathode catalyst layer (CL) is presented, which is validated with previous experimental data in terms of both performance and oxygen transport resistance. The model includes a 1D macroscopic description of proton, electron and oxygen transport across the CL thickness, which is locally coupled to a 1D microscopic model that describes oxygen transport toward Pt sites. Oxygen transport from the channel to the CL and ionic transport across the membrane are incorporated through integral boundary conditions. The model is complemented with data of effective transport and electrochemical properties extracted from multiple experimental works. The results show that the contribution of the thin ionomer film and Pt/ionomer interface increases with the inverse of the roughness factor. Whereas the contribution of the water film and the water/ionomer interface increases with the ratio between the geometric area and the surface area of active ionomer. Moreover, it is found that CLs diluted with bare carbon provide lower performance than non-diluted samples due to their lower electrochemical surface area and larger local oxygen transport resistance. Optimized design of non-diluted samples with a good distribution of the overall oxygen flux among Pt sites is critical to reduce mass transport losses at low Pt loading.

A parametric analysis is presented using a previously validated 1D model for a cathode catalyst layer (CL). The results show that maximum power density at low Pt loading can be maximized with relatively thin CLs (thickness ∼ 2 μm) featuring a high carbon volume fraction (low ionomer-to-carbon weight ratio, I/C) compared to high Pt loading CLs. The shift of the optimal carbon volume fraction (I/C ratio) is caused by the dominant role of the local oxygen transport resistance at low Pt loading, which is lowered by a reduction of the average ionomer film thickness (better ionomer distribution among carbon particles). In contrast, at high Pt loading, higher porosity and pore radius (lower carbon volume fraction) is beneficial due to an increase of bulk effective diffusivity despite thickening of ionomer films. Moreover, the results show that performance at low Pt loading is significantly improved with increasing mass-specific activity. The effect of average saturation and ionomer permeability on performance at low Pt loading is lower compared to dry CL composition and mass-specific activity.

Free volume plays a key role on transport in proton exchange membranes (PEMs), including ionic conduction, species permeation, and diffusion. Positron annihilation lifetime spectroscopy and electrochemical impedance spectroscopy are used to characterize the pore size distribution and ionic conductivity of synthesized PEMs from polysulfone/polyphenylsulfone multiblock copolymers with different degrees of sulfonation (SPES). The experimental data are combined with a bundle-of-tubes model at the cluster-network scale to examine water uptake and proton conduction. The results show that the free pore size changes little with temperature in agreement with the good thermo-mechanical properties of SPES. However, the free volume is significantly lower than that of Nafion^®, leading to lower ionic conductivity. This is explained by the reduction of the bulk space available for proton transfer where the activation free energy is lower, as well as an increase in the tortuosity of the ionic network.

Concentrated Solar Power (CSP) enables stable, dispatchable electricity generation through an integrated Thermal Energy Storage (TES) system, but current molten salt-based configurations are limited to ~565ºC, constraining efficiency and system integration. The COOPERANT project develops a novel high-temperature CSP-TES system operating up to 1,000ºC, combining advanced volumetric receivers, hybrid sensible-latent storage, and AI-based digital control. This approach enables coupling with next-generation power cycles such as supercritical steam Rankine, air Brayton and supercritical CO2 (sCO2) cycles, while addressing the challenges of component durability, cost, and sustainability. By integrating innovative materials, digital twins, and circular design principles, COOPERANT aims to enhance the efficiency, scalability, and commercial viability of CSP, contributing to a resilient and decarbonized energy system.