Force field-based molecular simulations were used to calculate thermal expansivities, heat capacities, and Joule− Thomson coefficients of binary (standard) hydrogen−water mixtures for temperatures between 366.15 and 423.15 K and pressures between 50 and 1000 bar. The mole fraction of water in saturated hydrogen−water mixtures in the gas phase ranges from 0.004 to 0.138. The same properties were calculated for pure hydrogen at 323.15 K and pressures between 100 and 1000 bar. Simulations were performed using the TIP3P and a modified TIP4P force field for water and the Marx, Vrabec, Cracknell, Buch, and Hirschfelder force fields for hydrogen. The vapor−liquid equilibria of hydrogen−water mixtures were calculated along the melting line of ice Ih, corresponding to temperatures between 264.21 and 272.4 K, using the TIP3P force field for water and the Marx force field for hydrogen. In this temperature range, the solubilities and the chemical potentials of hydrogen and water were obtained. Based on the computed solubility data of hydrogen in water, the freezing-point depression of water was computed ranging from 264.21 to 272.4 K. The modified TIP4P and Marx force fields were used to improve the solubility calculations of hydrogen− water mixtures reported in our previous study et al. J. Chem. Eng. Data 2019, 64, 4103−4115] for temperatures between 323 and 423 K and pressures ranging from 100 to 1000 bar. The chemical potentials of ice Ih were calculated as a function of pressure between 100 and 1000 bar, along the melting line for temperatures between 264.21 and 272.4 K, using the IAPWS equation of state for ice Ih. We show that at low pressures, the presence of water has a large effect on the thermodynamic properties of compressed hydrogen. Our conclusions may have consequences for the energetics of a hydrogen refueling station using electrochemical hydrogen compressors.

Today, humankind is confronted by a series of global challenges: energy/environmental crises, population growth, pandemics, and geopolitical wars, that simultaneously promote the depletion of natural resources and accelerate the contamination Energy security concerns require novel greener and more sustainable processes, and Paris Agreement goals have put in motion several measures aligned with the 2050 roadmap strategies and net zero emission goals. Renewable energies are a promising alternative to existing infrastructures, with solar energy one of the most appealing due to its use of the overabundant natural source of energy. Photocatalysis as a simple heterogeneous surface catalytic reaction is well placed to enter the realm of scaling up processes for wide scale implementation. Inspired by natural photosynthesis, artificial water splitting's beauty lies in its simplicity, requiring only light, a catalyst, and water. The bottlenecks to producing a high volume of hydrogen are several: Reactors with efficient photonic/mass/heat profiles, multifunctional efficient solar-driven catalysts, and proliferation of pilot devices. Three case studies, developed in Japan, Spain, and France are showcased to emphasize efforts on a pilot and large-scale examples. In order for solar-assisted photocatalytic H 2 to mature as a solution, the aforementioned bottlenecks must be overcome for the field to advance its technology readiness level, assess the capital expenditure, and enter the market.

In this article, we have brought a different perspective to the topic of mass transport losses in a proton exchange membrane (PEM) water electrolyzer, particularly regarding the role of water flow and the dominant mass transport mechanism in the porous transport layer (PTL). We conducted permeation experiments on a sintered Ti PTL, where we measured the pressure loss of gas that flows through its pores; furthermore, we presented a model based on the van Genuchten−Mualem capillary pressure and the Carman−Kozeny gas permeability, and we report an increase in the pressure loss with respect to the water flow, which we reported as an increase in the apparent tortuosity of the pores in the PTL. From this we conclude that the water flow exerts a shear stress on the gas flowing through the PTL, proportional to its kinetic energy, and that the gas permeation is the dominant transport mechanism within a PTL, in contrast to a one-or two-phase flow, which is more energy demanding. Finally, we propose that further work be carried out, in particular by comparing these results to in situ measurements on an operating PEM electrolyzer.

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