In this dataset, the search targets records classified under C25B11, C25B13 or B01J23 that also mention electrode material, Raney nickel, diaphragm material or catalyst coating in the title or claims. That combination captures the electrode alloys, separator/diaphragm chemistries and catalyst coatings used inside alkaline water electrolysis (AWE) cells, as distinct from PEM or solid-oxide electrolyzer materials which sit in different IPC groups. Practitioners searching this space should expect the bulk of relevant art to sit in C25B, with secondary art scattered across C25D electroplating and H01M fuel-cell classes.

Patent applications are typically published around 18 months after filing, so any year close to the data cut-off is still missing filings that haven't published yet. In this dataset the 2026 figure of 4 families is a partial-year snapshot, not a real drop-off, and even 2024–2025 figures should be read as provisional until later data cuts catch up. The reliable comparison point is the 2021 peak of 38 and the 2022 midpoint of 27, both of which are far enough back to be considered essentially complete.

The co-assignee network shows DE NORA PERMELEC and Yokohama National University filing jointly most often, with 54 shared families, followed by DE NORA PERMELEC with Kawasaki Heavy Industries at 40 and Yokohama National University with Kawasaki Heavy Industries at 23. That triangle dominates the most-cited documents in the corpus, including the top-cited diaphragm and bipolar-vessel patents. Beyond that cluster, recent-year momentum across the named assignees is flat or negative, suggesting the leading filers have slowed rather than accelerated their claim activity.

The IPC subclasses with the fewest records — G21F radiation shielding at 7, C01B inorganic compounds at 6, and B01D separation processes at 9 — are thin relative to the 249 records anchoring the core C25B electrolytic-cell class. None of the ten recorded co-assignee pairs bridges a diaphragm specialist with a filtration or inorganic-chemistry specialist, which points to an open combination: diaphragm materials engineered with integrated gas-separation or filtration functions. That gap sits adjacent to, rather than inside, the densely cited diaphragm and bipolar-vessel claims that dominate the landscape.

Not necessarily. Citation counts inside a searched corpus naturally favour older records because they have had more time to accumulate citations from later filings — the top-cited documents here, such as US4445994A from the early 1980s, are influential precedents rather than necessarily active commercial constraints. A better read is that high citation counts mark the technical routes (diaphragm chemistry, bipolar cell architecture, Ni-based cathodes) that later filers kept building on, which is useful for understanding lineage but should be checked against current assignee activity and legal status before drawing freedom-to-operate conclusions.