Rajiv Ramanujam Prabhakar, Sudhanshu Shukla, Haoyi Li, R. Soyoung Kim, Wei Chen, Jérôme Beaudelot, Jan D’Haen, Daniely Reis Santos, Philippe M. Vereecken, Gian-Marco Rignanese, Ethan J. Crumlin, Junko Yano, Bart Vermang and Joel W. Ager
{"title":"Origin of photoelectrochemical CO2 reduction on bare Cu(In,Ga)S2 (CIGS) thin films in aqueous media without co-catalysts†","authors":"Rajiv Ramanujam Prabhakar, Sudhanshu Shukla, Haoyi Li, R. Soyoung Kim, Wei Chen, Jérôme Beaudelot, Jan D’Haen, Daniely Reis Santos, Philippe M. Vereecken, Gian-Marco Rignanese, Ethan J. Crumlin, Junko Yano, Bart Vermang and Joel W. Ager","doi":"10.1039/D4EY00233D","DOIUrl":null,"url":null,"abstract":"<p >Photoelectrochemical (PEC) CO<small><sub>2</sub></small> reduction (CO<small><sub>2</sub></small>R) on semiconductors provides a promising route to convert CO<small><sub>2</sub></small> to fuels and chemicals. However, most semiconductors are not stable under CO<small><sub>2</sub></small>R conditions in aqueous media and require additional protection layers for long-term durability. To identify materials that would be stable and yield CO<small><sub>2</sub></small>R products in aqueous conditions, we investigated bare Cu(In,Ga)S<small><sub>2</sub></small> (CIGS) thin films. We synthesized CIGS thin films by sulfurizing a sputtered Cu–In–Ga metal stack. The as-synthesized CIGS thin films are Cu-deficient and have a high enough bandgap (1.7 eV) suitable to perform CO<small><sub>2</sub></small>R. The bare CIGS photocathodes had faradaic yields of 14% for HCOO<small><sup>−</sup></small> and 30% for CO in 0.1 M KHCO<small><sub>3</sub></small> electrolyte without the use of any co-catalysts under 1 sun illumination at an applied bias of −0.4 V <em>vs.</em> RHE and operated stably for 80 min. <em>Operando</em> Raman spectroscopy under CO<small><sub>2</sub></small>R conditions showed that the dominant A<small><sub>1</sub></small> mode of CIGS was unaffected during operation. Post-mortem X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analysis suggests that the CO<small><sub>2</sub></small>R stability could be related to self-protection caused by the <em>in situ</em> formation of oxides/hydroxides of Ga and In during operation. Density functional theory (DFT) calculations also reveal that Ga and In are the preferential sites for the adsorption of CO<small><sub>2</sub></small>R products, particularly HCOO<small><sup>−</sup></small>. These results show that CIGS is a promising semiconductor material for performing direct semiconductor/electrolyte reactions in aqueous media for the PEC CO<small><sub>2</sub></small>R.</p>","PeriodicalId":72877,"journal":{"name":"EES catalysis","volume":" 2","pages":" 327-336"},"PeriodicalIF":0.0000,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.rsc.org/en/content/articlepdf/2025/ey/d4ey00233d?page=search","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"EES catalysis","FirstCategoryId":"1085","ListUrlMain":"https://pubs.rsc.org/en/content/articlelanding/2025/ey/d4ey00233d","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Photoelectrochemical (PEC) CO2 reduction (CO2R) on semiconductors provides a promising route to convert CO2 to fuels and chemicals. However, most semiconductors are not stable under CO2R conditions in aqueous media and require additional protection layers for long-term durability. To identify materials that would be stable and yield CO2R products in aqueous conditions, we investigated bare Cu(In,Ga)S2 (CIGS) thin films. We synthesized CIGS thin films by sulfurizing a sputtered Cu–In–Ga metal stack. The as-synthesized CIGS thin films are Cu-deficient and have a high enough bandgap (1.7 eV) suitable to perform CO2R. The bare CIGS photocathodes had faradaic yields of 14% for HCOO− and 30% for CO in 0.1 M KHCO3 electrolyte without the use of any co-catalysts under 1 sun illumination at an applied bias of −0.4 V vs. RHE and operated stably for 80 min. Operando Raman spectroscopy under CO2R conditions showed that the dominant A1 mode of CIGS was unaffected during operation. Post-mortem X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analysis suggests that the CO2R stability could be related to self-protection caused by the in situ formation of oxides/hydroxides of Ga and In during operation. Density functional theory (DFT) calculations also reveal that Ga and In are the preferential sites for the adsorption of CO2R products, particularly HCOO−. These results show that CIGS is a promising semiconductor material for performing direct semiconductor/electrolyte reactions in aqueous media for the PEC CO2R.