Traditional imprudent approaches for carbon-based energy conversion and utilization have brought irreversible destruction to ecological cycles. The need for clean, efficient, and renewable energy alternatives has motivated governments and researchers to launch research projects with the aim of contributing to the realization of energy sustainability through theoretical and technological scientific breakthroughs. For example, in 2019, the National Natural Science Foundation of China started the Basic Science Center Program for “Order-ised Energy Conversion” (OEC). This project, led by Prof. Liejin Guo from the State Key Laboratory of Multiphase Flow in Power Engineering of Xi’an Jiaotong University of China, gathers many top energy-related research groups throughout China, particularly in the field of solar hydrogen/fuel production.

To further advance research in the field of solar hydrogen/fuel production, this special section of Volume 10, Issue 2 of the Journal of Photonics for Energy includes eight original research articles that address fundamental and applied aspects of solar-to-hydrogen or solar-to-fuel conversion. The special section is intended to present research in advanced nanomaterials, devices, and integrated systems for photocatalytic, photoelectrochemical, and photovoltaic solar hydrogen/solar liquid fuel production, as well as results related to interfacial and surface processes and reaction mechanisms. These areas are represented by several reports in this section. Naixu et al. demonstrate the enhanced photocatalytic ${\mathrm{CO}}_2$ reduction by the synthesis of Ni-doped mesoporous ${\mathrm{TiO}}_2$ nanocrystals with tablet morphologies, as well as the Ag cocatalyst. Jiangang et al. report the improvement of a series of 3-D ZnO/CdS photoelectrodes through a two-step hydrothermal approach with different cadmium precursors resulting from a 3-D structure with an opened-up, porous morphology. Yuzhou et al. investigate the effect of mixed-sacrificial reagents on hydrogen evolution over two typical photocatalysts, i.e., $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ and ${\mathrm{TiO}}_2$. Jian et al. report the excellent photocatalytic property of ${\mathrm{Fe}}_2{\mathrm{O}}_3/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ composite with the Z-scheme heterojunction. Penghui et al. compare the optical property, surface charge state, and photocatalytic behavior of ZnO with different exposure faces. Nana et al. investigate the effect of different pyrolysis temperature on electrocatalytic activities of the carbon fibers-coated Co@N-doped porous carbon derived from ZIF-67/alginate fibers. The section also features more applications with several reports on the investigations into photo transfer and photothermal systems. Linqi et al. demonstrate the characteristics of solar radiative transfer and participating media through analysis of aerosol particle samples from different weather conditions. Bo et al. report a photothermal polymethylsilsesquioxane-vinyltrimethoxysilane-polypyrrole xerogel for efficient solar-driven viscous oil/water separation through one-pot synthesis route.

It is hoped that the articles presented in this special section will provide some representative snapshots regarding aspects of solar hydrogen/fuel production, from material science to systems engineering.