Concerning catalytic materials in green hydrogen production journal articles and patents, the scope of several substance classes expanded appreciably in the 2010s and culminated in a peak of substance diversity in 2019. The slight dip in distinct substances from 2019-2021 contrasts with the continued overall increase in publication count (Figure ). In addition to the general increase in distinct substances, green hydrogen production had a primarily academic research focus in the first half of the decade but then had a gradual increase in the share of patents to reach 15% of the total publication volume in 2021. Based on these observations, green hydrogen production catalysis appears to be reaching maturity as a research field with commercial potential.