Nanostructured core-shell metal borides-oxides as highly efficient electrocatalysts for photoelectrochemical water oxidation

Can Lu; Palani R Jothi; Thomas Thersleff; Tetyana M Budnyak; Anna Rokicinska; Kunio Yubuta; Richard Dronskowski; Piotr Kuśtrowski; Boniface P T Fokwa; Adam Slabon

doi:10.1039/c9nr09818f

Nanostructured core-shell metal borides-oxides as highly efficient electrocatalysts for photoelectrochemical water oxidation

Nanoscale. 2020 Feb 7;12(5):3121-3128. doi: 10.1039/c9nr09818f. Epub 2020 Jan 22.

Authors

Affiliations

¹ Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany.
² Department of Chemistry and Center for Catalysis, University of California, Riverside, 92507 California, USA. bfokwa@ucr.edu.
³ Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius väg 16 C, 10691 Stockholm, Sweden. adam.slabon@mmk.su.se.
⁴ Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Krakow, Poland.
⁵ Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan.
⁶ Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany and Hoffmann Institute of Advanced Materials, Shenzhen Polytechnic, Liuxian Blvd 7098, 518055 Shenzhen, China.

PMID: 31965133
DOI: 10.1039/c9nr09818f

Abstract

Oxygen evolution reaction (OER) catalysts are critical components of photoanodes for photoelectrochemical (PEC) water oxidation. Herein, nanostructured metal boride MB (M = Co, Fe) electrocatalysts, which have been synthesized by a Sn/SnCl₂ redox assisted solid-state method, were integrated with WO₃ thin films to build heterojunction photoanodes. As-obtained MB modified WO₃ photoanodes exhibit enhanced charge carrier transport, amended separation of photogenerated electrons and holes, prolonged hole lifetime and increased charge carrier density. Surface modification of CoB and FeB significantly enhances the photocurrent density of WO₃ photoanodes from 0.53 to 0.83 and 0.85 mA cm^-2, respectively, in transient chronoamperometry (CA) at 1.23 V vs. RHE (V_RHE) under interrupted illumination in 0.1 M Na₂SO₄ electrolyte (pH 7), corresponding to an increase of 1.6 relative to pristine WO₃. In contrast, the pristine MB thin film electrodes do not produce noticeable photocurrent during water oxidation. The metal boride catalysts transform in situ to a core-shell structure with a metal boride core and a metal oxide (MO, M = Co, Fe) surface layer. When coupled to WO₃ thin films, the CoB@CoO_x nanostructures exhibit a higher catalytic enhancement than corresponding pure cobalt borate (Co-B_i) and cobalt hydroxide (Co(OH)_x) electrocatalysts. Our results emphasize the role of the semiconductor-electrocatalyst interface for photoelectrodes and their high dependency on materials combination.