Modulating Electronic Structure by Etching Strategy to Construct NiSe2 /Ni0.85 Se Heterostructure for Urea-Assisted Hydrogen Evolution Reaction

Exploring and developing novel strategies for constructing heterostructure electrocatalysts is still challenging for water electrolysis. Herein, a creative etching treatment strategy is adopted to construct NiSe2 /Ni0.85 Se heterostructure. The rich heterointerfaces between NiSe2 and Ni0.85 Se emerge strong electronic interaction, which easily induces the electron transfer from NiSe2 to Ni0.85 Se, and tunes the charge-state of NiSe2 and Ni0.85 Se. In the NiSe2 /Ni0.85 Se heterojunction nanomaterial, the higher charge-state Ni0.85 Se is capable of affording partial electrons to combine with hydrogen protons, inducing the rapid formation of H2 molecule. Accordingly, the lower charge-state NiSe2 in the NiSe2 /Ni0.85 Se heterojunction nanomaterial is more easily oxidized into high valence state Ni3+ during the oxygen evolution reaction (OER) process, which is beneficial to accelerate the mass/charge transfer and enhance the electrocatalytic activities towards OER. Theoretical calculations indicate that the heterointerfaces are conducive to modulating the electronic structure and optimizing the adsorption energy toward intermediate H* during the hydrogen evolution reaction (HER) process, leading to superior electrocatalytic activities. To expand the application of the NiSe2 /Ni0.85 Se-2h electrocatalyst, urea is served as the adjuvant to proceed with the energy-saving hydrogen production and pollutant degradation, and it is proven to be a brilliant strategy.

Dual Atoms (Fe, F) Co-Doping Inducing Electronic Structure Modulation of NiO Hollow Flower-Spheres for Enhanced Oxygen Evolution/Sulfion Oxidation Reaction Performance

Heteroatoms Fe, F co-doped NiO hollow spheres (Fe, F-NiO) are designed, which simultaneously integrate promoted thermodynamics by electronic structure modulation with boosted reaction kinetics by nano-architectonics. Benefiting from the electronic structure co-regulation of Ni sites by introducing Fe and F atoms in NiO , as the rate-determined step (RDS), the Gibbs free energy of OH* intermediates (ΔGOH* ) for Fe, F-NiO catalyst is significantly decreased to 1.87 eV for oxygen evolution reaction (OER) compared with pristine NiO (2.23 eV), which reduces the energy barrier and improves the reaction activity. Besides, densities of states (DOS) result verifies the bandgap of Fe, F-NiO(100) is significantly decreased compared with pristine NiO(100), which is beneficial to promote electrons transfer efficiency in electrochemical system. Profiting by the synergistic effect, the Fe, F-NiO hollow spheres only require the overpotential of 215 mV for OER at 10 mA cm-2 and extraordinary durability under alkaline condition. The assembled Fe, F-NiO||Fe-Ni2 P system only needs 1.51 V to reach 10 mA cm-2 , also exhibits outstanding electrocatalytic durability for continuous operation. More importantly, replacing the sluggish OER by advanced sulfion oxidation reaction (SOR) not only can realize the energy saving H2 production and toxic substances degradation, but also bring additional economic benefits.

Enabling Stable Zn Anodes by Molecularly Engineering the Inner Helmholtz Plane with Amphiphilic Dibenzenesulfonimide Additive

The notorious dendrite growth and hydrogen evolution reaction (HER) are considered as main barriers that hinder the stability of the Zn-metal anode. Herein, molecular engineering is conducted to optimize the inner Helmholtz plane with a trace of amphiphilic dibenzenesulfonimide (BBI) in an aqueous electrolyte. Both experimental and computational results reveal that the BBI^- binds strongly with Zn²⁺ to form {Zn(BBI)(H₂ O)₄ }⁺ in the electrical double layer and reduces the water supply to the Zn anode. During the electroplating process, {Zn(BBI)(H₂ O)₄ }⁺ is "compressed" to the Zn anode/electrolyte interface by Zn²⁺ flow, and accumulated and adsorbed on the surface of the Zn anode to form a dynamic water-poor inner Helmholtz plane to inhibit HER. Meanwhile, the{Zn(BBI)(H₂ O)₄ }⁺ on the Zn anode surface possesses an even distribution, delivering uniform Zn²⁺ flow for smooth deposition without Zn dendrite growth. Consequently, the stability of the Zn anode is largely improved with merely 0.02 M BBI^- to the common electrolyte of 1 M ZnSO₄ . The assembled Zn||Zn symmetric cell can be cycled for more than 1180 h at 5 mA cm^-2 and 5 mA h cm^-2 . Besides, the practicability in Zn||NaV₃ O₈ ·1.5 H₂ O full cell is evaluated, which suggests efficient storage even under a high mass loading of 12 mg cm^-2 .

Amorphous K-Buserite Microspheres for High-Performance Aqueous Zn-Ion Batteries and Hybrid Supercapacitors

Aqueous Zn-ion batteries (AZIBs) and Zn-ion hybrid supercapacitors (AZHSCs) are considered promising energy-storage alternatives to Li-ion batteries due to the attractive merits of low-price and high-safety. However, the lack of suitable cathode materials always hinders their large-scale application. Herein, amorphous K-buserite microspheres (denoted as K-MnO_x ) are reported as cathode materials for both AZIBs and AZHSCs, and the energy-storage mechanism is systematically revealed. It is found that K-MnO_x is composed of rich amorphous K-buserite units, which can irreversibly be transformed into amorphous Zn-buserite units in the first discharge cycle. Innovatively, the transformed Zn-buserite acts as active materials in the following cycles and is highly active/stable for fast Zn-diffusion and superhigh pseudocapacitance, enabling the achievement of high-efficiency energy storage. In the AZIBs, K-MnO_x delivers 306 mAh g^-1 after 100 cycles at 0.1 A g^-1 with 102% capacity retention, while in the AZHSCs, it shows 515.0/116.0 F g^-1 at 0.15/20.0 A g^-1 with 92.9% capacitance retention at 5.0 A g^-1 after 20 000 cycles. Besides, the power/energy density of AZHSCs device can reach up to 16.94 kW kg^-1 (at 20 A g^-1 )/206.7 Wh kg^-1 (at 0.15 A g^-1 ). This work may provide some references for designing next-generation aqueous energy-storage devices with high energy/power density.

Constructing Molybdenum Phosphide@Cobalt Phosphide Heterostructure Nanoarrays on Nickel Foam as a Bifunctional Electrocatalyst for Enhanced Overall Water Splitting

The construction of multi-level heterostructure materials is an effective way to further the catalytic activity of catalysts. Here, we assembled self-supporting MoS₂@Co precursor nanoarrays on the support of nickel foam by coupling the hydrothermal method and electrostatic adsorption method, followed by a low-temperature phosphating strategy to obtain Mo₄P₃@CoP/NF electrode materials. The construction of the Mo₄P₃@CoP heterojunction can lead to electron transfer from the Mo₄P₃ phase to the CoP phase at the phase interface region, thereby optimizing the charge structure of the active sites. Not only that, the introduction of Mo₄P₃ will make water molecules preferentially adsorb on its surface, which will help to reduce the water molecule decomposition energy barrier of the Mo₄P₃@CoP heterojunction. Subsequently, H* overflowed to the surface of CoP to generate H₂ molecules, which finally showed a lower water molecule decomposition energy barrier and better intermediate adsorption energy. Based on this, the material shows excellent HER/OER dual-functional catalytic performance under alkaline conditions. It only needs 72 mV and 238 mV to reach 10 mA/cm² for HER and OER, respectively. Meanwhile, in a two-electrode system, only 1.54 V is needed to reach 10 mA/cm², which is even better than the commercial RuO₂/NF||Pt/C/NF electrode pair. In addition, the unique self-supporting structure design ensures unimpeded electron transmission between the loaded nanoarray and the conductive substrate. The loose porous surface design is not only conducive to the full exposure of more catalytic sites on the surface but also facilitates the smooth escape of gas after production so as to improve the utilization rate of active sites. This work has important guiding significance for the design and development of high-performance bifunctional electrolytic water catalysts.

Temperature-Induced Structure Transformation from Co0.85Se to Orthorhombic Phase CoSe2 Realizing Enhanced Hydrogen Evolution Catalysis

Transition-metal chalcogenides (TMC) have been widely studied as active electrocatalysts toward the hydrogen evolution reaction due to their suitable d-electron configuration and relatively high electrical conductivity. Herein, we develop a feasible method to synthesize an orthorhombic phase of CoSe₂ (o-CoSe₂) from the regeneration of Co_0.85Se, where the temperature plays a key role in controlling the structure transformation. To the best of our knowledge, this is the first report about this synthetic route for o-CoSe₂. The resulting o-CoSe₂ catalysts exhibit enhanced hydrogen evolution reaction performance with an overpotential of 220 mV to reach 10 mA cm^-2 in 1.0 M KOH. Density functional theory calculations further reveal that the change in the Gibbs free energy of hydrogen, water adsorption energy, and the downshifted d-band center make o-CoSe₂ more suitable for accelerating the HER process.

Trace Amount of NiP2 Cooperative CoMoP Nanosheets Inducing Efficient Hydrogen Evolution

As a very attractive clean energy, hydrogen has a high energy density and great potential to achieve zero pollution emission. Therefore, the preparation of hydrogen evolution electrocatalysts with excellent performance is an urgent task to ameliorate the global energy shortage and environmental pollution. Here, a trace amount of NiP₂ coupled with CoMoP nanosheets (NCMP) was synthesized by the one-step hydrothermal method and low-temperature phosphidation. Studies have found that although the dosage of NiP₂ is very low, its appearance has been efficient to improve the hydrogen evolution reaction (HER) performance of CoMoP, which may be induced by the synergistic effect of the two different components NiP₂ and CoMoP. To find the superior catalyst, the effect of Ni content on the catalyst performance is also studied, and it is found that when the dosage of Ni is 0.02 mM, NCMP-2 (2 means 0.02 mM) displays the most outstanding overpotential (10 mA cm^-2) of 46 mV.