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Electrochemical Cycling‐Induced Amorphization of Cobalt(II,III) Oxide for Stable High Surface Area Oxygen Evolution Electrocatalysts
Author(s) -
Gupta Prashant Kumar,
Saha Sulay,
Gyanprakash Maurya,
Kishor Koshal,
S. Pala Raj Ganesh
Publication year - 2019
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201900880
Subject(s) - amorphous solid , oxygen evolution , electrochemistry , materials science , aqueous solution , intercalation (chemistry) , electrocatalyst , oxide , chemical engineering , inorganic chemistry , electrode , chemistry , crystallography , metallurgy , engineering
The activity of electrocatalysts critically depends on the chemical coordination around the active sites. Amorphous materials have short‐range atomic ordering while their crystalline counterparts have both short and long‐range ordering. Traditional synthesis of amorphous materials, involving quenching from high temperatures is unsuitable as it results in less porosity and surface area. In this context, room‐temperature syntheses of high surface area amorphous materials with high activity are desirable. Here, we contrast two electrochemical synthesis procedures for generating high surface area amorphous Co 3 O 4 at room temperature via electrochemical ion intercalation/deintercalation and surface oxidation/reduction cycles and evaluate their performance for electrocatalytic oxygen evolution reaction (OER). In the first approach, Li‐ion is used for the intercalation/deintercalation (Li/D−Li) cycles in Co 3 O 4 , which leads to expansion and contraction of structure, inducing amorphization of Co 3 O 4 by the pulverization of crystal structure in non‐aqueous medium. In the second approach, rapid electrochemical surface oxidation/reduction (Ox/Red) of Co 3 O 4 in the aqueous medium leads to the formation of a metastable amorphous structure. The OER specific activity (activity per unit electrochemical surface area) for Li/D−Li−Co 3 O 4 is ∼3.5 times and Ox/Red‐ Co 3 O 4 induced amorphization is ∼2.5 times higher than their crystalline Co 3 O 4 . The superior OER metrics of both the room‐temperature amorphization techniques are rationalized via the increase in the ratio of Co 2+ /Co 3+ obtained from the Co‐2p XPS spectra. Further, the decrease in overall polarization resistance per site for the OER reaction for both amorphous samples were analyzed from the Tafel plot and electrochemical impedance spectroscopy (EIS). In Li/D−Li−Co 3 O 4 , the Li‐ion intercalation in bulk Co 3 O 4 structure generates higher bulk‐oxygen vacancies leading to higher conductivity and reduction in overall charge‐transport resistance for electrocatalyst. On the other hand, Ox/Red‐ induced amorphization is restricted to the surface or near‐surface only with the formation of a small amount of metallic Co which hampers the OER.