One assignee leads the ranked field with 45 of the 302 records in scope, well ahead of the fifth-ranked assignee at 13 records. The top five assignees combined hold 120 records, 39.7% of the total, and the top ten extend that to 54.3%. Below the top ten there is a long tail of universities, national laboratories and smaller specialty firms each holding a handful of filings, so the field has a defined leadership group rather than being either monopolised or fully fragmented.

Filings peaked at 46 records in 2020 and declined to 10 by 2024, a 62% drop over that three-year span using the last years with complete data. That is a genuine cooling from the peak, not a permanent verdict on the technology’s prospects, since publication lags actual filing by roughly eighteen months and the 2025-2026 counts in this dataset are still incomplete. Anyone using this trend for a go/no-go decision should treat the most recent two years as provisional.

The dataset spans eight IPC subclasses, led by F28D heat-exchange apparatus at 34.8% of the 302 records, B01J chemical and catalytic processes at 23.2%, and C01B non-metallic elements and inorganic compounds at 16.9%. F24S solar collectors, H01M batteries, F25B refrigeration and heat pumps, and C01G metal compounds each cover smaller but still notable shares. Because records can carry multiple classes, these figures add up to more than 100% of the total and should be read as overlapping coverage, not a mutually exclusive breakdown.