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Lanthanum‐Based Compounds: Electronic Band‐Gap‐Dependent Electrocatalytic Materials for Oxygen Reduction Reaction
Author(s) -
Gu Weiwei,
Song Ye,
Liu Jingjun,
Wang Feng
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201701136
Subject(s) - chemistry , lanthanum , catalysis , inorganic chemistry , electrochemistry , oxygen , disproportionation , electrocatalyst , fermi level , adsorption , band gap , materials science , electrode , electron , organic chemistry , physics , optoelectronics , quantum mechanics
The electronic energy level of lanthanum compounds plays an important role in the oxygen reduction reaction (ORR) electrocatalytic process. In this work, three lanthanum compounds, LaOHCO 3 , La 2 O 2 CO 3 , and La 2 O 3 , have been synthesized through an in situ urea hydrolysis method, followed by annealing at different temperatures. Among these lanthanum compounds, the layer‐structured La 2 O 2 CO 3 has the smallest band gap and moderate values of the conduction band (CB) and valence band (VB). Electrochemical measurements in 0.1 m KOH solution have shown that, compared with the other catalysts, La 2 O 2 CO 3 exhibits the best electrocatalytic activity with the lowest H 2 O 2 production and highest durability for ORR, which proves the close correlation between electronic energy level and electrocatalytic ORR activity. During the ORR process over La 2 O 2 CO 3 , some covalent electrons from the VB are first excited to the CB and then transfer to the unoccupied π* 2p orbitals of an active oxygen molecule, leading to strengthened oxygen adsorption and promotion of the reduction of oxygen. Moreover, La 2 O 2 CO 3 has an ability to chemically disproportionate hydrogen peroxide (to give HO 2 − ), and the produced HO 2 − at the energy level of O 2 /HO 2 − can undergo prompt chemical disproportionation into O 2 and OH − . The O 2 generated at this stage is adsorbed on the catalyst surface, which can be utilized for further oxygen reduction.