Ni3Te2 has been reported as a highly efficient OER electrocatalyst with an overpotential of 180 mV at 10 mA cm−2 and also showing HER catalytic activity in alkaline medium.
Crystalline–amorphous phase boundary engineering can be an effective strategy to develop cost-effective and high-performance electrocatalysts for water splitting.
The
rational design of multifunctional catalysts that use non-noble
metals to facilitate the interconversion between H2, O2, and H2O is an intense area of investigation.
Bimetallic nanosystems with highly tunable electronic, structural,
and catalytic properties that depend on their composition, structure,
and size have attracted considerable attention. Herein, we report
the synthesis of bimetallic nickel–copper (NiCu) alloy nanoparticles
confined in a sp2 carbon framework that exhibits trifunctional
catalytic properties toward hydrogen evolution (HER), oxygen reduction
(ORR), and oxygen evolution (OER) reactions. The electrocatalytic
functions of the NiCu nanoalloys were experimentally and theoretically
correlated with the composition-dependent local structural distortion
of the bimetallic lattice at the nanoparticle surfaces. Our study
demonstrated a downshift of the d-band of the catalysts that adjusts
the binding energies of the intermediate catalytic species. XPS analysis
revealed that the binding energy for Ni 2p3/2 band of the
Ni0.25Cu0.75/C nanoparticles was shifted ∼3
times compared to other bimetallic systems, and this was correlated
to the high electrocatalytic activity observed. Interestingly, the
bimetallic Ni0.25Cu0.75/C catalyst surpassed
the OER performance of RuO2 benchmark catalyst exhibiting
a small onset potential of 1.44 V vs RHE and an overpotential of 400
mV at 10 mA·cm–2 as well as the electrochemical
long-term stability of commercial RuO2 and Pt catalysts
and kept at least 90% of the initial current applied after 20 000
s for the OER/ORR/HER reactions. This study reveals significant insight
about the structure–function relationship for non-noble bimetallic
nanostructures with multifunctional electrocatalytic properties.
The electrocatalytic performance of transition metal sulfide (TMS)− graphene composites has been simply regarded as the results of high conductivity and the large surface/volume ratio. However, unavoidable factors such as degree of oxidation of TMSs have been hardly considered for the origin of this catalytic activity of TMS−graphene composites. To accomplish the reliable application of TMS-based electrocatalytic materials, a clear understanding of the thermodynamic stability of TMS and effects of oxidation on catalytic activity is necessary. In addition, the mechanism of charge transfer at the TMS−graphene interface must be studied in depth to properly design composite materials. Herein, we report a comprehensive study of the physical chemistry at the junction of a Co 1−x Ni x S 2 −graphene composite, which is a prototype designed to unravel the mechanisms of charge transfer between TMS and graphene. Specifically, the thermodynamic stability and the effects of oxidation of TMSs during the oxygen evolution reaction (OER) on the reaction mechanism are systematically investigated using density functional theory (DFT) calculations and experimental observations. Cobalt atoms anchored on pyridinic N sites in the graphene support form metal−semiconductor (SC) junctions, and the internal band bending at these junctions facilitates electron transfer from TMSs to graphene. The junction enables fast sinking of the excess electron from OH − adsorbate. Partially oxidized amorphous TMS layers formed during the OER can facilitate adsorption and desorption of OH and H atoms, boosting the OER performance of TMS−graphene nanocomposites. From the DFT calculations, the enhanced electrocatalytic activity of TMS−graphene nanocomposites originates from two important factors: (i) increased internal band bending and (ii) parallelized OER pathways at the interface of pristine and oxidized TMSs.
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