An Interfacial Electron Transfer on Tetrahedral NiS2 /NiSe2 Heterocages with Dual-Phase Synergy for Efficiently Triggering the Oxygen Evolution Reaction.

Tetrahedral NiS2 /NiSe2 heterocages with rich-phase boundaries are synthesized through a simultaneous sulfuration/selenylation process using Ni-based acetate hydroxide prisms as precursor. Such a nanocage-like NiS2 /NiSe2 heterostructure can expose more active sites, accelerate the mass transport of the ions/gas, and optimize the interfacial electronic structure, which shows a significantly lower overpotential of 290 mV at 20 mA cm-2 than those of NiS/NiS2 and NiSe2 as counterparts. The experimental characterizations and theoretical density functional theory (DFT) calculations unveil that the interfacial electron transfer from NiSe2 to NiS2 at the heterointerface can modulate the electronic structure of NiS2 /NiSe2 , which further cooperates synergistically to change the Gibbs free energy of oxygen-containing intermediates as the rate-determining step (RDS) from 2.16 eV (NiSe2 ) and 2.10 eV (NiS2 ) to 1.86 eV (NiS2 /NiSe2 heterostructures) during the oxygen evolution reaction (OER) process. And as a result, tetrahedral NiS2 /NiSe2 heterocages with dual-phase synergy efficiently trigger the OER process, and accelerate the OER kinetics. This work provides insights into the roles of the interfacial electron transfer in electrocatalysis, and can be an admirable strategy to modulate the electronic structure for developing highly active electrocatalysts.

Synergistic coupling of heterostructured porous CoP nanosheets with P doped NiO for highly efficient overall alkaline water splitting.

Exploring non-noble metal materials as bifunctional catalysts for water electrolysis is of great significance for the development and utilization of hydrogen energy. Herein, a flower branch-leaf shaped phosphide/oxide heterogeneous electrocatalyst located on Ni foam (CoP/P-NiO/NF) was developed through hydrothermal and phosphorization strategy. Benefiting from the strong ability to dissociate H2O molecules on P-NiO and the suitable adsorption of intermediate H species on CoP, the optimal CoP/P-NiO/NF exhibited outstanding performance with low overpotentials of 52 mV at current density of 10 mA cm-2, smaller Tafel slopes of 73.6 mV dec-1 for hydrogen evolution reaction (HER). Meanwhile, CoP/P-NiO/NF indicated 265 mV at 100 mA cm-2 with Tafel slope of 101.8 mV dec-1 for oxygen evolution reaction (OER) due to the optimal redistribution of electrons among Ni2+, Co2+ and Co3+ for favorable adsorption/desorption of oxygen-intermediates. Both HER and OER shown robust stability during 32 h without decline. The corresponding two-electrode system for overall alkaline water splitting required a low voltage of 1.6 V at 100 mA cm-2 with long stability (20 h) which is far lower than that on RuO2-Pt/C and many other reported non-noble metal electrocatalysts. This work demonstrates that the synergistic effect and morphology engineering play vital roles in the enhanced electrocatalytic performance.

Doping Mo into NiFe LDH/NiSe Heterostructure to Enhance Oxygen Evolution Activity by Synergistically Facilitating Electronic Modulation and Surface Reconstruction.

It is of great significance to design highly efficient electrocatalysts with abundant earth elements instead of precious metals for water splitting. Herein, Mo-doped NiFe-layered double hydroxides/NiSe heterostructure (Mo-NiFe LDH/NiSe) was fabricated by coupling Mo-doped NiFe LDH and NiSe on nickel foam (NF). The heterostructure electrocatalyst showed ultra-low overpotential (250 mV) and remarkable durability for oxygen evolution reaction (OER) at 150 mA cm-2 . Both theoretical and experimental results confirmed that Mo doping and interfacial synergism induced the interfacial charge redistribution and the lifted d-band center to weaken the energy barrier (EB) of the formation of OOH* . Mo doping also facilitated the surface reconstruction of NiFe LDH into Ni(Fe)OOH as the active sites under electro-oxidation process. This work provides a facile strategy for electronic modulation and surface reconstruction of OER electrocatalyst by transition metal doping and heterostructure generation.

Hierarchical sheet-on-sheet heterojunction array of a ß-Ni(OH)2/Fe(OH)3 self-supporting anode for effective overall alkaline water splitting.

Rationally designing high-performance non-noble metal electrocatalysts is of essence to improve energy conversion efficiency in water splitting. Herein, a unique 3D hierarchical sheet-on-sheet heterojunction between Fe(OH)3 and ß-Ni(OH)2 on pretreated Ni foam (NiFe-HD/pre-NF) was fabricated by a two-step strategy involving the interfacial hydrolysis-deposition of Fe2+ and electrodeposition of Ni2+. The presence of the Ni-O-Fe bridge at the Fe(OH)3/ß-Ni(OH)2 heterointerface can induce interfacial electronic redistribution to form Ni3+ in NiFe-HD/pre-NF, and further strengthen the adsorption of OH- and weaken the O-H bond to change the rate-determining step (RDS) for accelerating OER kinetics. Benefiting from the sheet-on-sheet architecture and dual-phase synergism on NiFe-HD/pre-NF, the optimal NiFe-HD/pre-NF exhibits excellent OER performance with a lower overpotential of 256 mV at 100 mA cm-2, a small Tafel slope of 81 mV dec-1, high intrinsic activity and robust stability. Alkaline water-splitting using NiFe-HD/pre-NF as the anode requires ultralow cell voltages of 1.62 V and 1.83 V at current densities of 100 mA cm-2 and 400 mA cm-2, respectively, which are comparable with commercial alkaline water electrolysis, and operates steadily at a current density of 100 mA cm-2 for 85 h without decay. This work proposes a facile strategy for constructing heterojunctions and modulating electronic interaction to develop electrocatalysts with new architectures.

Electronic modulation and proton transfer by iron and borate co-doping for synergistically triggering the oxygen evolution reaction on a hollow NiO bipyramidal prism.

Designing an Earth-abundant and inexpensive electrocatalyst to drive the oxygen evolution reaction (OER) for high-purity hydrogen production is of great importance. Herein, the cation (iron) and anion (borate) co-doping strategy was proposed to effectively trigger the OER performance on a low-cost NiO material. The optimal hollow Fe/Bi-NiO bipyramidal prism shows superior OER performance, and displays a low overpotential (261 mV) at 10 mA cm-2, accompanied by a low Tafel slope (46 mV dec-1), excellent intrinsic activity and robust stability. The overall alkaline water splitting using Fe/Bi-NiO/NF as an anode affords low cell voltages of 1.50 and 1.63 V at 10 and 100 mA cm-2, and operates steadily at a high current density of 100 mA cm-2 for 55 h without decay. The excellent electrocatalytic activity could be ascribed to the hollow structure to shorten the mass transfer pathway, the electronic modulation by Fe doping, the increased accessible electroactive sites created by oxygen vacancies through borate doping, and the formation of BO33--OH- to accelerate the deprotonation of OHads.

Alkaline-Etched NiMgAl Trimetallic Oxide-Supported KMoS-Based Catalysts for Boosting Higher Alcohol Selectivity in CO Hydrogenation.

The acidity/alkalinity and structural properties of NiMgAl trimetallic oxides (MMOs) can be effectively modulated by the alkaline-etching process with various etching times, which are further used as a support to prepare KMoS-based catalysts through the cetyltrimethylammonium bromide-encapsulated Mo-precursor strategy. The enriched surface anion groups in alkaline-etched MMO affect the textural properties, metal-support interaction, and sulfidation degree of the as-synthesized KMoS-based catalysts. As a result, KMoS-based catalysts using alkaline-etched MMO as supports effectively enhance the reducibility and dispersion of Mo species, which exert a positive influence on higher alcohol synthesis (HAS) performance in CO hydrogenation. A proper balance between acidity/alkalinity and structural properties in K, Mo/MMO- x catalysts can significantly enhance the alcohol selectivity in HAS from 55 to 65% (carbon selectivity). The formation of C2+ alcohols can be boosted by adol condensation with optimal acidic/basic properties via suppressing the acidity and increasing the amount of basic sites. The alkaline-etching process also significantly improves the space time yield of C2+ alcohols over unit mass of molybdenum.