Experimental practices required to isolate thermal effects in plasmonic photo-catalysis: lessons from recent experiments

Metal nanoparticles have recently been shown experimentally to speed up chemical reactions when subject to illumination. The mechanisms of this phenomenon have been under debate. A dominant role for high energy non-thermal (typically but imprecisely referred to as “hot”) electrons was proposed in a study by the Halas group [Science 362, 69 (2018)]. However, evidence that the faster chemistry has a purely thermal origin has been accumulating, alongside the identification of methodological and technical flaws in the theory and experiments claiming the dominance of “hot” electrons [Science 364, 9367 (2019)]. Here, we advance this discussion towards the possibility of isolating thermal from non-thermal effects. We detail a series of experimental aspects that must be accounted for before effects of “hot” electrons can be distinguished from thermal contributions in plasmonic photocatalysis.