The most-cited records in this corpus are diaphragm patents, led by WO2013183584A1 at 87 citations and JP2015117417A at 78, both concentrated in ion-permeable membrane design for alkaline electrolysis cells. Asahi Kasei and De Nora Permelec are the assignees most closely associated with this diaphragm cluster, with De Nora Permelec also holding the dataset's two strongest co-assignee relationships. Because citation counts favour older filings, these documents should be read as foundational prior art that later filers built around, not necessarily as the newest technology available.

Filing volume rose from 30 in 2017 to a peak of 108 in 2024 before declining, and recent-year momentum data shows several major assignees, including Asahi Kasei and Kawasaki Heavy Industries, at 0 filings or -100% year-on-year. This pattern is consistent with a field where core claim positions on diaphragm chemistry and electrode design were established during the 2019-2024 window and are now being defended rather than extended. It does not necessarily mean commercial activity has slowed; publication lag of roughly 18 months also means the final one to two years in any filing trend understate true activity.

In this dataset, alkaline electrolysis claims cluster heavily around diaphragm materials, porosity and pore-size ratios, reflecting the mature liquid-electrolyte architecture. AEM-specific claims appear more often in the catalysis (B01J) and polymer processing (C08J) subclasses, since anion exchange membranes require different catalyst formulations and membrane polymer chemistry than a porous alkaline diaphragm. Both share the core C25B electrolytic production classification, which is why searches across this space need to separate diaphragm-based claims from membrane-polymer claims to avoid conflating the two architectures.

Secondary IPC volume outside the core C25B classification is comparatively light in dynamic operation control, non-noble bifunctional catalyst coatings, and gas crossover mitigation at high current density. These branches show up in the dataset's B01J and B01D counts but at a fraction of the volume seen in diaphragm-specific C25B claims, suggesting less-crowded claim space for filers targeting renewables-coupled or high-current-density operation rather than base diaphragm chemistry. Any first claim there should be checked against the existing diaphragm cluster to confirm it does not depend on a covered separator architecture.

China leads receiving-office volume in this corpus with 192 filings, followed by the European Patent Office at 166, the United States at 102, WIPO/PCT filings at 78, Japan at 59 and India at 47. This ordering reflects both manufacturing capacity build-out and the location of the diaphragm and electrode specialists driving much of the historical filing volume. Companies assessing freedom-to-operate risk should treat China and Europe as the two jurisdictions carrying the largest live document counts to clear.