Photoelectrochemical (PEC) water splitting, particularly self-biased PEC systems, holds great promise for solar energy utilization. However, the limited transparency of most photoelectrodes presents challenges in fabricating tandem photoelectrodes with photovoltaic (PV) cells for self-biased water splitting. Herein, a novel self-biased hybrid system integrating photoelectrodes (TiO₂, BiVO₄), beam splitters (BSs), and PV cell was proposed to enhance solar energy utilization and PEC water splitting performance. The results indicate that the integration of BSs significantly improves the current densities of both self-biased PV-PEC systems and single PEC systems. The current density of self-biased water splitting system with BSs exceeds that of the conventional TiO₂ + BVO-PV system, and the intersection point of the I–V curves for the photoanodes and solar cell is closer to the maximum power output of the solar cell. The effective utilization of the solar spectrum by both the photoelectrode and the PV cell in the hybrid system with BSs significantly increases the power output by a factor of 18.8 compared to the conventional tandem self-biased system. The predicted results indicate that the hydrogen production rate of the system with BSs is 12.1 µmol/(h∙cm²), while the STH efficiency is enhanced by a factor of 12.38 and 19.87 compared to conventional TiO₂ + BVO-PV and TiO₂/BVO-PV tandem PV-PEC systems, respectively, demonstrating the advantage of the water splitting system with spectral BSs. In conclusion, this work provides an innovative approach of achieving self-biased water splitting by coupling spectral BSs with a PV-PEC system, resulting in improved solar energy harvesting efficiency.

Japan aims to establish an international hydrogen supply chain by utilizing low-cost and abundantly available hydrogen sources and liquid hydrogen carriers to realize a future hydrogen economy that will enhance energy security and help achieve carbon neutrality. While hydrogen does not emit CO₂ when used as a fuel to generate energy, CO₂ emissions can be attributed to hydrogen due to the energy and other resources required at each stage of the hydrogen supply chain. Therefore, from a life cycle perspective, if hydrogen is to contribute to the world’s carbon neutrality goal, the entire hydrogen supply chain must be low-carbon. This paper explores the life cycle CO₂ emissions of international hydrogen supply chains envisaged by Japan. The target supply chains involve hydrogen produced from renewable electricity via electrolysis, as well as from fossil fuels with carbon capture and storage, sourced from resource-rich countries and imported to Japan using liquid hydrogen carriers such as liquid hydrogen, methylcyclohexane (MCH), and ammonia (NH₃). In addition, this paper addresses potential options for reducing life cycle CO₂ emissions to effectively establish a low-carbon hydrogen supply chain.

The curved bending regions of serpentine flow channels play a crucial role in mass transfer and the overall performance of the flow field in proton exchange membrane fuel cells (PEMFCs). This paper proposes a “2D Topology-Curvature Optimization” progressive design method to optimize the bend area structures, aiming to enhance PEMFC performance. Through numerical simulations, it compares the topology-curvature optimization model with both the algorithm-based optimization model and a validation model, and analyzes the mass transfer, heat transfer characteristics, and output performance of PEMFC under different flow fields. The results indicate that the optimized structures improve convection and diffusion within the flow field, effectively enhancing the transport and distribution of oxygen and water within the PEMFC. Performance improvements, ranked from highest to lowest, are TS-III > MD-G (Model-GA) > MD-P (Model-PSO) > TS-II > TS-I. Among the optimized models, TS-III (Topology Structure-III) exhibits the greatest increases in peak current density and peak power density, with improvement of 4.72% and 3.12%, respectively. When considering the relationship between performance improvement and pressure drop using the efficiency evaluation criterion (EEC), TS-II demonstrates the best overall performance.

Direct air capture (DAC) is an emerging technology aimed at mitigating global warming. However, conventional DAC technologies and the subsequent utilization processes are complex and energy-intensive. An integrated system of direct air capture and utilization (IDACU) via in-situ catalytic conversion to fuels and chemicals is a promising approach, although it remains in the early stages of development. This review examines the current technical routes of IDACU, including solid-based dual-functional materials (DFMs) through thermo-catalysis, IDACU using liquid sorbents with thermo-catalysis, and non-thermal conversion methods. It covers the basic principles, reaction conditions, main products, material types, and the existing problems and challenges associated with these technical routes. Additionally, it discusses the recent advancements in solid-based DFMs for IDACU, with particular attention to the differences in material characteristics between carbon capture from flue gases (ICCU) and DAC. While IDACU technology holds significant promise, it still faces numerous challenges, especially in the design of advanced materials.