Mapping Japan’s innovation activity in hydrogen technologies: An approach based on patent network analysis

Hydrogen is central to Japan’s strategy for carbon neutrality, energy security, and industrial competitiveness. This article examines hydrogen-related technological development through patent network analysis of applications filed by major Japanese firms between 1960 and 2024. Using PATENTSCOPE data and IPC co-occurrence networks, it maps the technological domains, organizational actors, and knowledge linkages shaping Japan’s hydrogen innovation system. The findings show strong concentration in fuel cells, hydrogen production and storage, and vehicle applications. Central IPC codes cover electrochemical energy conversion, non-metallic compounds, electric propulsion, electrolysis, catalysis, and compressed-gas storage. Honda, Toyota, Panasonic, Nissan, Mitsubishi Heavy Industries, Toshiba, and Hitachi emerge as leading actors, underscoring the role of automotive and heavy-industry firms. Overall, Japan’s trajectory reflects a coordinated ecosystem in which state policy, corporate R&D, and demonstration projects reinforce technological specialization. Yet dependence on imported energy and low-carbon hydrogen raises persistent concerns about cost competitiveness, green hydrogen deployment, and long-term decarbonization outcomes.