CoP as an acid-stable active electrocatalyst for the hydrogen-evolution reaction

Electrochemical synthesis, interfacial characterization and performance evaluation

Fadl H. Saadi, Azhar I. Carim, Erik Verlage, John C. Hemminger, Nathan S Lewis, Manuel P. Soriaga

Research output: Contribution to journalArticle

128 Citations (Scopus)

Abstract

Films of CoP have been electrochemically synthesized, characterized, and evaluated for performance as a catalyst for the hydrogen-evolution reaction (HER). The film was synthesized by cathodic deposition from a boric acid solution of Co2+ and H2PO2 - on copper substrates followed by operando remediation of exogenous contaminants. The films were characterized structurally and compositionally by scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectrophotometry. The catalytic activity was evaluated by cyclic voltammetry and chronopotentiometry. Surface characterization prior to electrocatalysis indicated that the film consisted of micrometer-sized spherical clusters located randomly and loosely on a slightly roughened surface. The composition of both the clusters and surface consisted of cobalt in the metallic, phosphide, and amorphous-oxide forms (CoO·Co2O3) and of phosphorus as phosphide and orthophosphate. The orthophosphate species, produced by air-oxidation, were eliminated upon HER electrocatalysis in sulfuric acid. The operando film purification yielded a functional electrocatalyst with a Co:P stoichiometric ratio of 1:1. After the HER, the surface was densely packed with micrometer-sized, mesa-like particles whose tops were flat and smooth. The CoP eletrodeposit exhibited an 85 mV overvoltage (η) for the HER at a current density of 10 mA cm-2 and was stable under operation in highly acidic solution, with an increase in η of 18 mV after 24 h of continuous operation. The comparative HER catalytic performance of CoP, film or nanoparticles, is as follows: ηPtCoP film = ηCoP NP, ηNi2P <ηCoSe2 <ηMoS2 <ηMoSe2.

Original languageEnglish
Pages (from-to)29294-29300
Number of pages7
JournalJournal of Physical Chemistry C
Volume118
Issue number50
DOIs
Publication statusPublished - Dec 18 2014

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electrochemical synthesis
electrocatalysts
Electrocatalysts
Hydrogen
acids
Acids
evaluation
hydrogen
Electrocatalysis
phosphides
micrometers
Phosphates
boric acids
overvoltage
Boric acid
Spectrophotometry
mesas
sulfuric acid
spectrophotometry
Cobalt

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

CoP as an acid-stable active electrocatalyst for the hydrogen-evolution reaction : Electrochemical synthesis, interfacial characterization and performance evaluation. / Saadi, Fadl H.; Carim, Azhar I.; Verlage, Erik; Hemminger, John C.; Lewis, Nathan S; Soriaga, Manuel P.

In: Journal of Physical Chemistry C, Vol. 118, No. 50, 18.12.2014, p. 29294-29300.

Research output: Contribution to journalArticle

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abstract = "Films of CoP have been electrochemically synthesized, characterized, and evaluated for performance as a catalyst for the hydrogen-evolution reaction (HER). The film was synthesized by cathodic deposition from a boric acid solution of Co2+ and H2PO2 - on copper substrates followed by operando remediation of exogenous contaminants. The films were characterized structurally and compositionally by scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectrophotometry. The catalytic activity was evaluated by cyclic voltammetry and chronopotentiometry. Surface characterization prior to electrocatalysis indicated that the film consisted of micrometer-sized spherical clusters located randomly and loosely on a slightly roughened surface. The composition of both the clusters and surface consisted of cobalt in the metallic, phosphide, and amorphous-oxide forms (CoO·Co2O3) and of phosphorus as phosphide and orthophosphate. The orthophosphate species, produced by air-oxidation, were eliminated upon HER electrocatalysis in sulfuric acid. The operando film purification yielded a functional electrocatalyst with a Co:P stoichiometric ratio of 1:1. After the HER, the surface was densely packed with micrometer-sized, mesa-like particles whose tops were flat and smooth. The CoP eletrodeposit exhibited an 85 mV overvoltage (η) for the HER at a current density of 10 mA cm-2 and was stable under operation in highly acidic solution, with an increase in η of 18 mV after 24 h of continuous operation. The comparative HER catalytic performance of CoP, film or nanoparticles, is as follows: ηPt <ηCoP film = ηCoP NP, ηNi2P <ηCoSe2 <ηMoS2 <ηMoSe2.",
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