Structure-Property Relationship of Defect-Trapped Pt Single-Site Electrocatalysts for the Hydrogen Evolution Reaction

Single-site catalysts (SSCs) have attracted significantresearchinterest due to their high metal atom utilization. Platinum singlesites trapped in the defects of carbon substrates (trapped Pt-SSCs)have been proposed as efficient and stable electrocatalysts for thehydrogen evolution reaction (HER). However, the correlation betweenPt bonding environment, its evolution during operation, and catalyticactivity is still unclear. Here, a trapped Pt-SSC is synthesized bypyrolysis of H2PtCl6 chemisorbed on a polyanilinesubstrate. In situ heated scanning transmission electron microscopyand temperature-dependent X-ray photoelectron spectroscopy clarifythe thermally induced structural evolution of Pt during pyrolysis.The results show that the nitrogen in polyaniline coordinates withPt ions and atomically disperses them before pyrolysis and traps Ptsites at pyridinic N defects generated during the substrate graphitization.Operando X-ray absorption spectroscopy confirms that the trapped Pt-SSCis stable at the HER working potentials but with inferior electrocatalyticactivity compared with metallic Pt nanoparticles. First principlecalculations suggest that the inferior activity of trapped Pt-SSCsis due to their unfavorable hydrogen chemisorption energy relativeto metallic Pt(111) surfaces. These results further the understandingof the structure-property relationship in trapped Pt-SSCs andmotivate a detailed techno-economic analysis to evaluate their commercialapplicability.