title: Observation of charge transfer cascades in α-Fe2O3/IrOxphotoanodes by operando X-ray absorption spectroscopy.
abstract: Electrochemical devices for energy conversion and storage are central for a sustainable economy. The performance of electrodes is driven by charge transfer across different layer materials and an understanding of the mechanistics is pivotal to gain improved efficiency. Here, we directly observe the transfer of photogenerated charge carriers in a photoanode made of hematite (α-Fe2O3) and a hydrous iridium oxide (IrOx) overlayer, which plays a key role in photoelectrochemical water oxidation. Through the use of operando X-ray absorption spectroscopy (XAS), we probe the change in occupancy of the Ir 5d levels during optical band gap excitation of α-Fe2O3. At potentials where no photocurrent is observed, electrons flow from the α-Fe2O3photoanode to the IrOxoverlayer. In contrast, when the composite electrode produces a sustained photocurrent (i.e., 1.4 V vs. RHE), a significant transfer of holes from the illuminated α-Fe2O3to the IrOxlayer is clearly demonstrated. The analysis of the operando XAS spectra further suggests that oxygen evolution actually occurs both at the α-Fe2O3/electrolyte and α-Fe2O3/IrOxinterfaces. These findings represent an important outcome for a better understanding of composite photoelectrodes and their use in photoelectrochemical systems, such as hydrogen generation or CO2reduction from sunlight.
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano Via Golgi 19, 20133 Milano, Italy. alessandro.minguzzi@unimi.it and Istituto Nazionale di Scienza e Tecnologia dei Materiali - INSTM, Via Giusti 9, Firenze, Italy.
authors.forename: Alessandro
authors.identifier: http://orcid.org/0000-0002-8130-4465
authors.initials: A
authors.lastname: Minguzzi
authors.affiliation: CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Naldoni
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano Via Golgi 19, 20133 Milano, Italy. alessandro.minguzzi@unimi.it.
authors.forename: Ottavio
authors.initials: O
authors.lastname: Lugaresi
authors.affiliation: Dipartimento di Chimica, Università di Pavia, Viale Taramelli 16, 27100, Pavia, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Achilli
authors.affiliation: CNR-Istituto Officina dei Materiali (IOM)-OGG, c/o ESRF-71, Avenue des Martyrs, 38043 Grenoble, France.
authors.forename: Francesco
authors.initials: F
authors.lastname: D'Acapito
authors.affiliation: CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Malara
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano Via Golgi 19, 20133 Milano, Italy. alessandro.minguzzi@unimi.it and Istituto Nazionale di Scienza e Tecnologia dei Materiali - INSTM, Via Giusti 9, Firenze, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Locatelli
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano Via Golgi 19, 20133 Milano, Italy. alessandro.minguzzi@unimi.it and Istituto Nazionale di Scienza e Tecnologia dei Materiali - INSTM, Via Giusti 9, Firenze, Italy and CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Vertova
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano Via Golgi 19, 20133 Milano, Italy. alessandro.minguzzi@unimi.it and Istituto Nazionale di Scienza e Tecnologia dei Materiali - INSTM, Via Giusti 9, Firenze, Italy and CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy.
authors.forename: Sandra
authors.initials: S
authors.lastname: Rondinini
authors.affiliation: Istituto Nazionale di Scienza e Tecnologia dei Materiali - INSTM, Via Giusti 9, Firenze, Italy and Dipartimento di Chimica, Università di Pavia, Viale Taramelli 16, 27100, Pavia, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ghigna