The most-cited records in this dataset are steam-reformer patents with internal hydrogen purification, led by US5861137A with 928 citations and US5997594A with 558. These establish the architecture where reforming and purification happen within a single reactor unit, and later membrane and adsorption filings largely build on that foundation rather than replacing it. Beyond the citation leaders, filing volume is spread across Japanese energy companies, Chinese research institutes and individual inventors, with no single assignee holding a dominant share of the 253 tracked families.

Filing activity is flat rather than growing: it peaked at 21 families in 2021 and held at 21 through the 2022 midpoint before easing off. That plateau suggests the core purification architectures — palladium membrane construction, PSA cycle design, reformer-integrated purification — are already well claimed, and new filings are refining details rather than opening new ground. Recent-year figures are also understated because publication typically lags filing by around 18 months, so the true 2025-2026 filing rate will only become clear later.

Palladium membrane purification uses a thin palladium or palladium-alloy layer that selectively passes hydrogen atoms while blocking other gases, giving very high purity output but at higher material cost and with durability limits under thermal cycling. Pressure swing adsorption (PSA) instead cycles gas through adsorbent beds that capture impurities at high pressure and release them at low pressure, trading some purity and recovery rate for lower capital cost and no precious-metal dependency. This dataset shows both routes actively claimed, with palladium membrane fabrication methods and PSA cycle/energy-penalty claims each carrying meaningful filing volume under B01D and C01B.

China leads by receiving-office volume with 95 filings in this dataset, ahead of the United States at 47, the European Patent Office at 37, and Japan at 20. That places China's filing volume above any other single jurisdiction tracked here, which has implications for both freedom-to-operate checks and licensing strategy in this field. Teams evaluating this space should not rely on US and EPO searches alone.

US20050109609A1 claims a method for forming a supported palladium membrane for hydrogen purification, specifically a sequence of providing a support, filling it with a metal, electroless plating a palladium membrane using a palladium salt solution, and then DC sputtering a further palladium membrane layer onto the support. The claim is a fabrication process, not the membrane material itself, so it primarily constrains parties using this specific electroless-plating-plus-sputtering combination rather than palladium membrane fabrication generally. Alternative fabrication routes, such as single-step sputtering or electroplating without the sputtered overlayer, would need to be checked separately against the wider membrane-fabrication prior art.