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Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

ABSTRACT: Transition-metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co-P films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self-limited layer-by-layer growth, and the deposited Co-P films were highly pure and smooth. The Co-P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co-P films prepared by the traditional post-phosphorization method. Moreover, the deposition of ultrathin Co-P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three-dimensional (3D) architectures.

SUBMITTER: Zhang H

PROVIDER: S-EPMC7540345 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

Zhang Haojie H Hagen Dirk J DJ Li Xiaopeng X Graff Andreas A Heyroth Frank F Fuhrmann Bodo B Kostanovskiy Ilya I Schweizer Stefan L SL Caddeo Francesco F Maijenburg A Wouter AW Parkin Stuart S Wehrspohn Ralf B RB

Angewandte Chemie (International ed. in English) 20200807 39

Transition-metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co-P films were deposited by using PH<sub>3</sub> plasma as the phosphorus source and an extra H<sub>2</sub> plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self-limited layer-by-layer growth, and the deposited Co-P films were highly pure and smooth. The Co-P films deposited via ALD exhibited better electrochemical and photoelectrochem ...[more]

PMID: 32608102

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Project description:The development of efficient and stable earth-abundant water oxidation catalysts is vital for economically feasible water-splitting systems. Cobalt phosphate (CoPi)-based catalysts belong to the relevant class of nonprecious electrocatalysts studied for the oxygen evolution reaction (OER). In this work, an in-depth investigation of the electrochemical activation of CoPi-based electrocatalysts by cyclic voltammetry (CV) is presented. Atomic layer deposition (ALD) is adopted because it enables the synthesis of CoPi films with cobalt-to-phosphorous ratios between 1.4 and 1.9. It is shown that the pristine chemical composition of the CoPi film strongly influences its OER activity in the early stages of the activation process as well as after prolonged exposure to the electrolyte. The best performing CoPi catalyst, displaying a current density of 3.9 mA cm-2 at 1.8 V versus reversible hydrogen electrode and a Tafel slope of 155 mV/dec at pH 8.0, is selected for an in-depth study of the evolution of its electrochemical properties, chemical composition, and electrochemical active surface area (ECSA) during the activation process. Upon the increase of the number of CV cycles, the OER performance increases, in parallel with the development of a noncatalytic wave in the CV scan, which points out to the reversible oxidation of Co2+ species to Co3+ species. X-ray photoelectron spectroscopy and Rutherford backscattering measurements indicate that phosphorous progressively leaches out the CoPi film bulk upon prolonged exposure to the electrolyte. In parallel, the ECSA of the films increases by up to a factor of 40, depending on the initial stoichiometry. The ECSA of the activated CoPi films shows a universal linear correlation with the OER activity for the whole range of CoPi chemical composition. It can be concluded that the adoption of ALD in CoPi-based electrocatalysis enables, next to the well-established control over film growth and properties, to disclose the mechanisms behind the CoPi electrocatalyst activation.

Dataset Information

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

Publications

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

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