For electrochemical CO2 reduction to HCOOH, an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density (JHCOOH) at a low overpotential. Indium oxide is good HCOOH production catalyst but with low conductivity. In this work, we report a unique corn design of In2O3-x@C nanocatalyst, wherein In2O3-x nanocube as the fine grains dispersed uniformly on the carbon nanorod cob, resulting in the enhanced conductivity. Excellent performance is achieved with 84% Faradaic efficiency (FE) and 11 mA cm−2JHCOOH at a low potential of − 0.4 V versus RHE. At the current density of 100 mA cm−2, the applied potential remained stable for more than 120 h with the FE above 90%. Density functional theory calculations reveal that the abundant oxygen vacancy in In2O3-x has exposed more In3+ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In3+ as the active site and the key intermediate of HCOO* during the process of CO2 reduction to HCOOH.
Sodium
layered oxides always suffer from sluggish kinetics and
deleterious phase transformations at deep-desodiation state (i.e., >4.0 V) in O3 structure, incurring inferior rate
capability
and grievous capacity degradation. To tackle these handicaps, here,
a configurational entropy tuning protocol through manipulating the
stoichiometric ratios of inactive cations is proposed to elaborately
design Na-deficient, O3-type Na
x
TmO2 cathodes. It is found that the electrons surrounding the
oxygen of the TmO6 octahedron are rearranged by the
introduction of MnO6 and TiO6 octahedra in Na-deficient
O3-type Na0.83Li0.1Ni0.25Co0.2Mn0.15Ti0.15Sn0.15O2−δ (MTS15) with expanded O–Na–O
slab spacing, giving enhanced Na+ diffusion kinetics and
structural stability, as disclosed by theoretical calculations and
electrochemical measurements. Concomitantly, the entropy effect contributes
to the improved reversibility of Co redox and phase-transition behaviors
between O3 and P3, as clearly revealed by ex situ synchrotron X-ray absorption spectra and in situ X-ray diffraction. Notably, the prepared entropy-tuned MTS15 cathode
exhibits impressive rate capability (76.7% capacity retention at 10
C), cycling stability (87.2% capacity retention after 200 cycles)
with a reversible capacity of 109.4 mAh g–1, good
full-cell performance (84.3% capacity retention after 100 cycles),
and exceptional air stability. This work provides an idea for how
to design high-entropy sodium layered oxides for high-power density
storage systems.
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