Are Sacrificial Agents a Sustainable Practice in Scalable Photocatalytic Hydrogen Production from Water?

Abstract

The rapid expansion of green hydrogen production is vital for decarbonizing hard-to-abate sectors. Photocatalytic water splitting, which generates hydrogen directly from sunlight and water, has therefore attracted major research attention. Yet translating this promise into scalable reality requires re-examining how photocatalysts are studied and benchmarked. A long-standing laboratory practice involves the use of sacrificial agents (SAs), such as alcohols, sulfides, or amines that act as hole scavengers to facilitate the hydrogen evolution reaction (HER). While this approach has accelerated catalyst discovery and mechanistic understanding, it differs fundamentally from true overall water splitting (OWS), where HER and the oxygen evolution reaction (OER) occur simultaneously. In SA-assisted systems, the oxidation half-reaction is replaced by sacrificial oxidation chemistry, making their performance metrics unsuitable for direct extrapolation to practical solar-fuel generation. Nevertheless, publications on SA-driven HER continue to outpace those on genuine OWS. Here, we argue that sustained reliance on SAs risks diverting resources, delaying innovation, and weakening confidence in photocatalytic hydrogen as a scalable climate solution. We advocate for greater recognition, support and increased focus on emerging alternatives that bridge laboratory discovery with sustainable OWS, fostering a constructive methodological shift toward practical solar-hydrogen technologies.