Self-Assembled Coral-like Hierarchical Architecture Constructed by NiSe2 Nanocrystals with Comparable Hydrogen-Evolution Performance of Precious Platinum Catalyst

Metal-free carbon-based porous materials, promising electrocatalysts for hydrogen fuel production

The development of effective and sustainable electrocatalysts for hydrogen fuel production is crucial for advancing clean energy technologies. Metal-free porous carbon materials have emerged as promising alternatives to traditional metal-based catalysts due to their low cost, high surface area, tunable porosity, and excellent electrochemical stability. This review provides a comprehensive overview of the latest advancements in metal-free porous carbon electrocatalysts for the hydrogen evolution reaction (HER). A comprehensive discussion is provided regarding how heteroatom doping, defect engineering, and surface functionalization improve catalytic activity. Additionally, we compare the performance of these materials and highlight recent strategies for improving their efficiency and durability. Future perspectives on optimizing metal-free porous carbons for large-scale hydrogen production are also explored. This review intends to give a clear view on the rational design of next-generation electrocatalysts for sustainable hydrogen energy applications.

Integrating NiSe2-MoSe2 heterojunctions with N-doped porous carbon substrate architecture for an enhanced electrocatalytic water splitting device

The development of sustainable energy technologies relies on the exploitation of efficient and durable electrocatalysts for water splitting at high current densities. Our work presents a novel bifunctional catalyst, denoted as NM@NC/CC, which combines the benefits of NiSe2-MoSe2 heterojunctions with nitrogen-enriched porous carbon derived from metal-organic frameworks (MOFs). The integration of these components is designed to harness their combined advantages, which include enhanced electron transfer, improved mass and gas evolution dynamics, and an increased number of catalytically active sites. These features collectively optimize the energetics for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, the catalyst facilitates rapid kinetics for the overall water-splitting process. The NM@NC/CC demonstrates low overpotentials, requiring only 91 mV for the HER and 280 mV for the OER to reach a current density of 10 mA cm-2. Even at higher current densities of 100 mA cm-2 for HER and 50 mA cm-2 for OER, the overpotentials are only 159 mV and 350 mV, respectively. Additionally, a two-electrode setup using this catalyst achieves a current density of 10 mA cm-2 with a minimal cell voltage of 1.56 V. The insights gained from this study will contribute to the advancement of electrocatalysts for energy conversion technologies.

Spherical cluster heterojunction engineering of NiFeP/g-C3N4 for efficient oxygen evolution reaction in alkaline solution

The construction of heterojunctions can reduce the energy barrier for the oxygen evolution reaction (OER), which is crucial for the design of efficient electrocatalysts. A novel OER electrocatalyst, composed of g-C3N4-supported NiFeP spherical nanoclusters, was successfully synthesized using a simple hydrothermal method and a gas-phase precipitation method. Benefiting from its unique spherical nanocluster structure and strong electronic interactions among Ni, Fe, and P, the catalyst exhibited outstanding performance under alkaline conditions, with an overpotential of only 232 mV at a current density of 10 mA cm-2 and a Tafel slope of 103 mV dec-1. Additionally, the electrical resistance of NiFeP/g-C3N4 (Rct = 5.1 Ω) was much lower than that of NiFeP (Rct = 10.8 Ω) and layered g-C3N4 (Rct = 44.8 Ω). The formation of a Schottky barrier heterojunction efficiently reduced electron transfer impedance during the OER process, accelerating the electron transfer from g-C3N4 to NiFeP, enhancing the carrier concentration, and thereby improving the OER activity. Moreover, The robust g-C3N4 chain-mail protects NiFeP from adverse reaction environments, maintaining a balance between catalytic activity and stability. Furthermore, ab initio molecular dynamics (AIMD) and density functional theory (DFT) were conducted to explore the thermal stability and internal electron transfer behavior of the cluster heterojunction structure. This study offers a broader design strategy for the development of transition metal phosphide (TMPs) materials in the oxygen evolution reaction.

Size-Dependent Graphene Support for Decorating Gold Nanoparticles as a Catalyst for Hydrogen Evolution Reaction with Machine Learning-Assisted Prediction

Size-dependent two-dimensional (2D) materials (e.g., graphene) have been recently used to improve their performance in various applications such as membrane filtration, energy storage, and electrocatalysts. It has also been demonstrated that 2D nanosheets can be one of the promising support materials for decorating nanoparticles (NPs). However, the optimum nanosheet size (lateral length and thickness) for supporting NPs has not yet been explored to enhance their catalytic performance. Herein, we elucidate the mechanism behind size-dependent graphene (GP) as a support due to which gold nanoparticles (AuNPs) are used as an active catalyst for the hydrogen evolution reaction (HER). Surprisingly, the decoration of AuNPs increased with the increasing nanosheet size, counter to what is widely reported in the literature (high surface area for smaller nanosheet size). We found that a large graphene nanosheet (lGP; ∼800 nm) used as the AuNP support (lGP/AuNPs) exhibited superior performance for the HER with long-term stability. The lGP/AuNPs with a suitable content of AuNPs provides a low overpotential and a small Tafel slope, being lower than that of other reported carbon-based HER electrocatalysts. This results from highly exposed active sites of well-dispersed AuNPs on lGP giving high conductivity. The laminar structure of the stacked graphene nanosheets and the high wettability of the lGP/AuNPs electrode surface also play crucial roles in enhancing electrolytes for penetration in the electrode, suggesting a highly electrochemical surface area. Moreover, machine learning (Random Forest) was also used to reveal the essential features of the advanced catalytic material design for catalyst-based applications.

Rational design of NiO/NiSe2@C heterostructure as high-performance anode for Li-ion battery

Biphasic or multiphase heterostructures have promising futures in advanced electrode materials for energy-related applications because of their desirable synergistic effects. Here we prepared a rational NiO/NiSe₂@C heterostructure microsphere through carbonization, selenization, and oxidation using Ni-MOF as a precursor. Electrochemical studies were conducted to examine the Li⁺ storage characteristics, and density functional theory (DFT) was utilized to comprehend the underlying mechanism. When employed as the anode for LIBs, the NiO/NiSe₂@C showed a high specific capacity and long-term cyclic stability, with a specific capacity of 992 mAh g^-1 for 600 cycles at a current density of 0.2 A g^-1. The NiO/NiSe₂@C exhibits a significantly enhanced lithium-ion diffusion coefficient ( [Formula: see text] ) value. The DFT results show that an electron-rich area forms at the NiO/NiSe₂ heterointerface, where the metalloid selenium transfers electrons to the oxygen atoms. The lithiation reactions were improved dramatically by redistributing interfacial charges, which can trigger a built-in electric field that dramatically promotes the capacitance contribution of electrode materials, enhances the lithium storage capacity, and accelerates the ion/electron transmission. The rational synthesis of NiO/NiSe₂@C heterostructure can provide an idea for designing novel heterostructure anode materials.

Metal-Organic Framework-Based Photocatalysis for Solar Fuel Production

Metal-organic frameworks (MOFs) represent a novel class of crystalline inorganic-organic hybrid materials with tunable semiconducting behavior. MOFs have potential for application in photocatalysis to produce sustainable solar fuels, owing to their unique structural advantages (such as clarity and modifiability) that can facilitate a deeper understanding of the structure-activity relationship in photocatalysis. This review takes the photocatalytic active sites as a particular perspective, summarizing the progress of MOF-based photocatalysis for solar fuel production; mainly including three categories of solar-chemical conversions, photocatalytic water splitting to hydrogen fuel, photocatalytic carbon dioxide reduction to hydrocarbon fuels, and photocatalytic nitrogen fixation to high-energy fuel carriers such as ammonia. This review focuses on the types of active sites in MOF-based photocatalysts and discusses their enhanced activity based on the well-defined structure of MOFs, offering deep insights into MOF-based photocatalysis.

MoS2 nanosheets vertically grown on CoSe2 hollow nanotube arrays as an efficient catalyst for the hydrogen evolution reaction

Although the design and synthesis of efficient electrocatalysts for the hydrogen evolution reaction (HER) are highly desirable, severe challenges still need to be addressed. Herein, ultrathin MoS₂ nanosheets were vertically grown on CoSe₂ hollow nanotube arrays via a simple three-step hydrothermal reaction by using carbon cloth (CC) as a substrate and were subsequently used as a highly efficient HER electrocatalyst (MoS₂@CoSe₂-CC hybrid). The MoS₂ nanosheets uniformly self-assembled on conductive CoSe₂ nanotube arrays exhibited a hierarchical and well-ordered structure. Such a unique structure may not only comprise more exposed active sites, but also enable fast electrolyte penetration and facilitate H⁺/electron transportation to accelerate the reduction and evolution of H₂ during the electrocatalytic process. As an HER electrocatalyst with a novel three-dimensional hierarchical structure, the MoS₂@CoSe₂-CC hybrid exhibited an outstanding catalytic HER performance with a small Tafel slope of 67 mV dec^-1 in alkaline media, while only requiring a low HER overpotential of 101 mV at 10 mA cm^-2. Notably, the MoS₂@CoSe₂-CC hybrid also demonstrated exceptional electrochemical durability and structural stability even after 1000 cycles or 48 h of continuous electrolysis. Overall, this work presents a new approach for the design and synthesis of robust, highly active, and cost-effective electrocatalysts for hydrogen generation.

Electronic regulation of a core–shell NiSe2 catalyst by Co doping to accelerate hydrogen evolution

A Co-doping core–shell shaped NiSe2 based catalyst (NixCo1−xSe2@NC) exhibits promising electrocatalytic activity for HER with a low overpotential of −143 mV at −10 mA cm−2, a small Tafel slope of 37.5 mV dec−1.

Selenium-induced NiSe2@CuSe2 hierarchical heterostructure for efficient oxygen evolution reaction

Electrochemical water splitting is widely studied in the hope of solving environmental deterioration and energy shortage. The design of inexpensive metal catalysts exhibiting desired catalytic performance and durable stability for efficient oxygen evolution is the pursuit of sustainable and clean energy fields. Herein, a three-dimensional (3D) flower-like NiSe₂ primary structure, modified with highly dispersed CuSe₂ nanoclusters as the secondary structure, is obtained by regulating the growth trend of the nanosheets. Benefiting from the metallicity of selenides and the formation of a heterogeneous interface, NiSe₂@CuSe₂/NF shows comparable performance toward the oxygen evolution reaction (OER) in an alkaline environment. Upon regulating the synthesis conditions, the catalyst exhibits its optimal performance with ultralow overpotential for the OER when the Ni/Cu molar ratio is 1 : 0.2 and the hydrothermal temperature and hydrothermal time are 200 °C and 6 h, respectively. It provides a current density of 10 mA cm^-2 when a potential of 201 mV is applied without iR compensation. In this work, the hierarchical heterostructures of NiSe₂ and CuSe₂ are synthesized, which exhibit high electrocatalytic activity towards the oxygen evolution reaction and provides a new possibility for the extensive application of copper-based compounds in advanced energy fields.

Enhancing the Electrochemical Performance of Sodium-Ion Batteries by Building Optimized NiS2 /NiSe2 Heterostructures

NiS_1.23 Se_0.77 nanosheets closely attached to the internal surface of hollow mesoporous carbon sphere (HMCS) to form a NiS_1.23 Se_0.77 nanosheets embedded in HMCS (NSSNs@HMCS) composite as the anode of sodium ion batteries (SIBs) is reported by a facile synthesis route. The anode exhibits a superior reversible capacity (520 mAh g^-1 at 0.1 A g^-1 )_, impressive coulombic efficiency (CE) of up to 95.3%, a high rate capacity (353 mAh g^-1 at 5.0 A g^-1 ), excellent capacity retention at high current density (95.6%), and high initial coulombic efficiency (ICE) (95.1%). Firstly, the highest ICE for NiS₂ /NiSe₂ -based anode can be ascribed to ultrathin layered structure of NiS_1.23 Se_0.77 nanosheet and highly efficient electron transfer between the active material and HMCS. Secondly, the optimized NiS₂ /NiSe₂ heterostructure at the nanoscale of the inside HMCS is formed after the first discharge/charge cycles, which can provide rich heterojunction interfaces/boundaries of sulfide/selenides to offer faster Na⁺ pathways, decrease the Na⁺ diffusion barriers, increase electronic conductivity, and limit the dissolution of polysulfides or polyselenides in the electrolyte. Finally, the hollow structure of the HMCS accommodates the volume expansion, prevents the pulverization and aggregation issues of composite materials, which can also promote outstanding electrochemical performance.

2D coordination polymer-derived CoSe2-NiSe2/CN nanosheets: the dual-phase synergistic effect and ultrathin structure to enhance the hydrogen evolution reaction

The evolution of cost-effective hydrogen evolution reaction (HER) electrocatalysts is of great significance for the development of clean energy. Exploring effective synthesis strategies to optimize the performance of non-noble metal electrocatalysts has always attracted our attention. Herein, ultrathin coordination polymers were used as precursors to controllably synthesize two-dimensional (2D) ultrathin dual-phase transition metal selenide (TMSs)/carbon-nitrogen (CN) composites (CoSe2-NiSe2/CN) by a two-step method (first a low temperature hydrothermal method for selenization, and then high temperature calcination selenization). Benefiting from its large specific surface area (49 m2 g-1), abundant catalytically active sites and synergistic effects, CoSe2-NiSe2/CN can significantly enhance the HER catalytic activity and exhibits good electrocatalytic activity with an overpotential of 150 mV at -10 mA cm-2, and a small Tafel slope of 42 mV dec-1 in an acidic electrolyte for the HER. This work provides a new strategy for optimizing the HER catalytic activity of TMSs by preparing 2D ultrathin dual-phase TMS composite materials.

Self-assembled CoSe2-FeSe2 heteronanoparticles along the carbon nanotube network for boosted oxygen evolution reaction

Water electrolysis is a significant alternative technique to produce clean hydrogen fuel in order to replace environmentally destructive fossil fuel combustion. However, the sluggish oxygen evolution kinetics makes this process vulnerable as it requires relatively high overpotentials. Hence, significantly effective electrocatalysts are necessary to access the water-oxidation process at a low overpotential to make this process industrially viable. Therefore, in order to reduce the energy barrier, we developed bimetallic CoSe2-FeSe2 heteronanoparticles along the carbon nanotube network (CoSe2-FeSe2/CNT) via a facile selenization strategy. Due to the unique assembly of highly conductive nanoparticles along the CNT network, the CoSe2-FeSe2/CNT displays an exceptionally good oxygen evolution (OER) activity; it requires 248 mV overpotential to reach a current density of 10 mA cm-2 (η10) with an ultra-low Tafel slope of 36 mV dec-1 and displays an overpotential of 1.59 V (η10) in the full water-splitting catalysis with the commercial Pt/C cathode. The high OER activity of CoSe2-FeSe2/CNT over the monometallic CoSe2/CNT and FeSe2/CNT electrocatalysts approve the synergistic interactions. Therefore, the superior performance is possibly ascribed to the unique porous nanoarchitecture and the strong coupling interactions between CoSe2 and FeSe2 heteronanoparticles on the conductive network. This study introduces an innovative approach to rationally design and fabricate cost-effective and highly proficient electrocatalysts for boosted OER performance.

Synergistic effect of cocatalytic NiSe2 on stable 1T-MoS2 for hydrogen evolution

Robust and economical catalysts are imperative to realize the versatile applications of hydrogen. Herein, a 1T-MoS2/N-doped NiSe2 composite was rationally synthesized via a solvothermal method, in which the MoS2 nanosheets have a stable 1T phase structure, and the NiSe2 nanoparticles serve as a cocatalytic support for MoS2. The nonnegligible electronic couplings between NiSe2 and MoS2 could facilitate the optimization of their electronic structure and then improve the hydrogen adsorption. What is more, the nitrogen dopants in the NiSe2 nanoparticles could intensify the intercalation of ammonium ions in the 1T-MoS2 nanosheets, and further enlarge their interlayer spacing, thus the electrolyte could infiltrate into the catalyst more easily and sufficiently. This work provides a new route for rationally designing highly active and low cost hydrogen evolution reaction (HER) catalysts, and enriches the study of transition metal chalcogenides toward HER.

Hydrothermal Synthesis of Polyhedral Nickel Sulfide by Dual Sulfur Source for Highly-Efficient Hydrogen Evolution Catalysis

Transition metal sulfides are cheap and efficient catalysts for water splitting to produce hydrogen; these compounds have attracted wide attention. Nickel sulfide (NiS₂) has been studied in depth because of its simple preparation process, excellent performance and good stability. Here, we propose a modification to the hydrothermal synthesis method for the fabrication of a highly efficient and stable NiS₂ electrocatalyst prepared by two different sulfur sources, i.e., sulfur powder and C₃H₇NaO₃S₂ (MPS), for application in hydrogen evolution reactions. The obtained NiS₂ demonstrated excellent HER performance with an overpotential of 131 mV to drive -10 mA cm^-1 in 0.5 M H₂SO₄ solution with 5mV performance change after 1000 cycles of stability testing. We believe that this discovery will promote the industrial development of nonprecious metal catalysts.

Two-Dimensional Metallic NiSe2 Nanoclusters-Based Low-Cost, Flexible, Amperometric Sensor for Detection of Neurological Drug Carbamazepine in Human Sweat Samples

Here we report a low-cost, flexible amperometric sensing platform for highly selective and sensitive detection of carbamazepine (CBZ) in human sweat samples. Detailed morphological characterization of the two-dimensional transition metal dichalcogenide NiSe₂, synthesized using one-step hydrothermal method, confirms the formation of dense NiSe₂ nanoclusters in the range of 500–650 nm, whereas X-ray diffraction and X-ray photoelectron spectroscopy studies reveal a stable and pure cubic crystalline phase of NiSe₂. The sensor device is fabricated by uniformly depositing an optimized weight percentage of as-synthesized NiSe₂ onto flexible and biocompatible polyimide substrate using spin coating, and metal contacts are established using thermal evaporation technique. The sensor exhibits a remarkable sensitivity of 65.65 μA/nM over a wide linear range of 50 nM to 10 μM CBZ concentrations and a low limit of detection of 18.2 nM. The sensing mechanism and excellent response of NiSe₂ toward CBZ can be attributed to the highly conductive metallic NiSe₂, large electroactive surface area of its nanoclusters, and highly interactive Ni²⁺/Ni³⁺ oxidation states. Furthermore, the presence of 10-fold excess of capable interferents, such as lactic acid, glucose, uric acid, and ascorbic acid, does not affect the accurate determination of CBZ, thus demonstrating excellent selectivity. The real-time detection of CBZ is evaluated in human sweat samples using standard addition method, which yields reliable results. Furthermore, the sensor shows excellent robustness when subject to bending cycles and fast response time of 2 s. The strategy outlined here is useful in developing sensing platforms at low potential without the use of enzymes or redox binders for applications in healthcare.

NiSe2-anchored N, S-doped graphene/Ni foam as a free-standing bifunctional electrocatalyst for efficient water splitting

It is still challenging to develop non-precious free-standing bifunctional electrocatalysts with high efficiency for hydrogen and oxygen evolution reactions. Herein, for the first time, we present a novel hybrid electrocatalyst synthesized via a facile hydrothermal reaction, which is constructed from ultrafine NiSe2 nanoparticles/nanosheets homogeneously anchored on 3D graphene/nickel foam (NiSe2/3DSNG/NF). This hybrid delivers superior catalytic performances for hydrogen/oxygen evolution reactions and overall water splitting: it shows an ultra-small Tafel slope of 28.56 mV dec-1 for hydrogen evolution in acid, and a small Tafel slope of 42.77 mV dec-1 for the oxygen evolution reaction; particularly, in a two-electrode setup for water splitting, it requires an ultra-small potential of 1.59 V to obtain 10 mA cm-2 with nearly 100% faradaic efficiencies for H2 and O2. This study presents a new approach of catalyst design and fabrication to achieve highly efficient and low-cost water electrolysis.

Ni2P/rGO/NF Nanosheets As a Bifunctional High-Performance Electrocatalyst for Water Splitting

The hydrogen generated via the water splitting method is restricted by the high level of theoretical potential exhibited by the anode. The work focuses on synthesizing a bifunctional catalyst with a high efficiency, that is, a nickel phosphide doped with the reduced graphene oxide nanosheets supported on the Ni foam (Ni₂P/rGO/NF), via the hydrothermal approach together with the calcination approach specific to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The Raman, X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscope (TEM), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM), as well as elemental mapping, are adopted to study the composition and morphology possessed by Ni₂P/rGO/NF. The electrochemical testing is performed by constructing a parallel two-electrode electrolyzer (Ni₂P/rGO/NF||Ni₂P/rGO/NF). Ni₂P/rGO/NF||Ni₂P/rGO/NF needs a voltage of only 1.676 V for driving 10 mA/cm², which is extremely close to Pt/C/NF||IrO₂/NF (1.502 V). It is possible to maintain the current density for no less than 30 hours. It can be demonstrated that Ni₂P/rGO/NF||Ni₂P/rGO/NF has commercial feasibility, relying on the strong activity and high stability.

Platinum nanoparticles on defect-rich nitrogen-doped hollow carbon as an efficient electrocatalyst for hydrogen evolution reactions

Design and synthesis of efficient electrocatalysts with low usage of precious metal and of high stability are essential for their practical applications in hydrogen evolution reactions. In this work, we synthesize an electrocatalyst through the deposition of platinum nanoparticles on defect-rich nitrogen-doped hollow carbon derived from surface-attached poly(4-vinylpyridine) monolayers. The platinum nanoparticles with an average diameter of about 1.8 nm are well dispersed on the outer surface of the pre-synthesized carbon material and the platinum loading is about 8.6 wt%. The mass activity of the as-synthesized catalyst under an overpotential of 55 mV is about 5.0 A mg_Pt⁻¹, about 4.93 times higher than that of commercial Pt/C catalysts. Moreover, the synthesized catalyst is also more electrochemically stable than commercial Pt/C catalysts as evidenced by continuous cyclic voltammetry and chronoamperometric response measurements.

Design and synthesis of efficient electrocatalysts with low usage of precious metal and of high stability are essential for hydrogen evolution reaction in their practical applications.

NiSe2/CdS composite nanoflakes photocatalyst with enhanced activity under visible light

Degrading organic pollutants using a photocatalyst under visible light is one of the effective ways to solve the increasingly serious environmental pollution problem. In this work, we have loaded a small amount of NiSe₂ nanoflakes on the surface of CdS using a simple and low-cost solvothermal synthesis method. The samples were characterized with detailed X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), photocurrent, photoluminescence spectrometer (PL), photocatalytic properties, etc. The results show that a 2 mol% load of NiSe₂ increases the rate of degradation of Rhodamine B (RhB) to more than twice the original rate (0.01000 min⁻¹versus 0.00478 min⁻¹). Meanwhile, the sample has excellent stability. The improved photocatalytic properties can be attributed to the face-to-face contact between the nanoflakes, accelerated separation and transfer of photon-generated carriers. This work provides a suitable co-catalyst that can be used to optimize the performance of other photocatalytic materials.

The obtained NiSe₂/CdS composite nanoflakes exhibit greatly enhanced photocatalytic properties due to the accelerated separation of photon-generated carriers.

The one-pot synthesis of porous Ni0.85Se nanospheres on graphene as an efficient and durable electrocatalyst for overall water splitting

Ni_0.85Se/RGO composite exhibits extraordinary water splitting.

3D hollow Co-Fe-P nanoframes immobilized on N,P-doped CNT as an efficient electrocatalyst for overall water splitting

The rational design of nonprecious and high-efficiency bifunctional electrocatalysts with advanced structural and compositional preponderance for water electrolysis is of paramount importance for the generation of sustainable and clean energy. Herein, for the first time, a novel three-dimensional (3D) hollow hybrid electrocatalyst, Co-Fe-P nanoframe immobilized on N,P-doped carbon nanotubes (CoFeP NFs/NPCNT), was synthesized by selectively etching a CNT-composited Co,Fe-based Prussian blue analogue and subsequent phosphorization. Benefiting from its unique 3D hollow nanoarchitecture, which offers rich porosity and abundant catalytically active sites and guarantees excellent conductivity and structural stability, the hollow CoFeP NFs/NPCNT hybrid delivered pronounced catalytic activity for oxygen evolution (or hydrogen evolution) in alkaline electrolyte, with a low overpotential of 278 (or 132) mV at 10 mA cm-2, small Tafel slope of 39.5 (or 62.9) mV dec-1 and prominent long-term stability. Therefore, when CoFeP NFs/NPCNT was employed as the cathode and anode toward overall water-splitting, it required a quite small cell voltage of only 1.56 V to afford a current density of 10 mA cm-2, and displayed outstanding electrocatalytic stability over 60 h, greatly approaching the performance of the commercial Pt/C(-)//RuO2(+) electrolyzer and outperforming most other non-noble-based electrolyzers.

High-Performance Ru@C4N Electrocatalyst for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

We report a high-performance Ru@C₄N electrocatalyst for the hydrogen evolution reaction (HER) in both acidic and alkaline solutions. This catalyst is synthesized by annealing a complex of a covalent organic framework compound coordinated with ruthenium synthesized by a "one-pot" solvothermal method. This Ru@C₄N catalyst shows excellent electrocatalytic activity toward the hydrogen evolution reaction (HER) in both acidic and alkaline solutions with very low overpotentials at 10 mA/cm² (6 mV in 0.5 M H₂SO₄ solution; 7 mV in 1.0 M KOH solution), which outperforms the commercial catalyst Pt/C. The Ru@C₄N electrocatalyst also exhibits high HER turnover frequencies of 0.93 H₂ per s in 0.5 M H₂SO₄ and 0.65 H₂ per s in 1.0 M KOH solutions at 25 mV as well as superior performance stability.

Ultrathin Ti3C2Tx (MXene) Nanosheet-Wrapped NiSe2 Octahedral Crystal for Enhanced Supercapacitor Performance and Synergetic Electrocatalytic Water Splitting

Metal selenides, such as NiSe₂, have exhibited great potentials as multifunctional materials for energy storage and conversation. However, the utilization of pure NiSe₂ as electrode materials is limited by its poor cycling stability, low electrical conductivity, and insufficient electrochemically active sites. To remedy these defects, herein, a novel NiSe₂/Ti₃C₂T_x hybrid with strong interfacial interaction and electrical properties is fabricated, by wrapping NiSe₂ octahedral crystal with ultrathin Ti₃C₂T_x MXene nanosheet. The NiSe₂/Ti₃C₂T_x hybrid exhibits excellent electrochemical performance, with a high specific capacitance of 531.2 F g^-1 at 1 A g^-1 for supercapacitor, low overpotential of 200 mV at 10 mA g^-1, and small Tafel slope of 37.7 mV dec^-1 for hydrogen evolution reaction (HER). Furthermore, greater cycling stabilities for NiSe₂/Ti₃C₂T_x hybrid in both supercapacitor and HER have also been achieved. These significant improvements compared with unmodified NiSe₂ should be owing to the strong interfacial interaction between NiSe₂ octahedral crystal and Ti₃C₂T_x MXene, which provides enhanced conductivity, fast charge transfer as well as abundant active sites, and highlight the promising potentials in combinations of MXene with metal selenides for multifunctional applications such as energy storage and conversion.

Cobalt-Tannin-Framework-Derived Amorphous Co-P/Co-N-C on N, P Co-Doped Porous Carbon with Abundant Active Moieties for Efficient Oxygen Reactions and Water Splitting

It remains a tremendous challenge to develop a low-cost, earth-abundant, and efficient catalyst with multifunctional activities for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Herein, a facile and scalable avenue was developed to prepare amorphous Co-P/Co-N-C supported on N, P co-doped porous carbon (Co-P/Co-N-C/NPC) with a large specific surface area (1462.9 m²  g^-1 ) and abundant reactive sites including Co-P, Co-N and NPC. The prepared electrocatalyst exhibits outstanding catalytic performance for HER (η=234 mV at 10 mA cm^-2 ), OER (η=374 mV at 10 mA cm^-2 ), and ORR (E_1/2 =0.89 V, vs. reversible hydrogen electrode). Benefiting from the excellent HER performance and outstanding OER activity, the Co-P/Co-N-C/NPC delivers a current density of 10 mA cm^-2 for overall water splitting at a cell voltage of 1.59 V, which is comparable with the IrO₂ -Pt/C couple electrode.

Hierarchical NiSe2 spheres composed of tiny nanoparticles for high performance asymmetric supercapacitors

To achieve superior performance of electrode materials, the design of rational and advantageous hierarchical structures has been confirmed as an effective and feasible approach.

A MOF-derived coral-like NiSe@NC nanohybrid: an efficient electrocatalyst for the hydrogen evolution reaction at all pH values

A coral-like NiSe@NC nanohybrid as an effective electrocatalyst for the hydrogen evolution reaction (HER) at all pH values, constructed via the in situ selenation of a Ni-MOFs precursor, is reported. The electrocatalyst shows overpotentials of 123 mV, 250 mV and 300 mV in 0.5 M H2SO4, 1.0 M KOH and 1.0 M PBS, respectively, to afford a current density of 10 mA cm-2. Meanwhile, NiSe@NC also exhibits a small Tafel slope and superior long-term stability over a wide pH range. The excellent electrocatalytic performance should be ascribed to the unique coral-like structure with a large BET specific surface area (125.4 m2 g-1) and mesoporous features, as well as synergistic effects between NiSe nanocrystals and highly conductive N-doped porous carbon.

Novel Cobalt-Doped Ni0.85Se Chalcogenides (Co xNi0.85- xSe) as High Active and Stable Electrocatalysts for Hydrogen Evolution Reaction in Electrolysis Water Splitting

In this paper, novel cobalt-doped Ni_0.85Se chalcogenides (Co _xNi_{0.85- x}Se, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co_0.1Ni_0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co_0.1Ni_0.75Se/rGO shows even better performance than unsupported Co_0.1Ni_0.75Se, which are confirmed by the reduction of HER overpotential of Co_0.1Ni_0.75Se/rGO to 103 mV compared to 153 mV of Co_0.1Ni_0.75Se at a current density of 10 mA/cm², and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co_0.1Ni_0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co_0.1Ni_0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.

Orthorhombic NiSe2 Nanocrystals on Si Nanowires for Efficient Photoelectrochemical Water Splitting

Photocatalytic water splitting is a vital technology for clean renewable energy. Despite enormous progress, the search for earth-abundant photocatalysts with long-term stability and high catalytic activity is still an important issue. We report three possible polymorphs of nickel selenide (orthorhombic phase NiSe₂, cubic phase NiSe₂, and hexagonal phase NiSe) as bifunctional catalysts for water-splitting photoelectrochemical (PEC) cells. Photocathodes or photoanodes were fabricated by depositing the nickel selenide nanocrystals (NCs) onto p- or n-type Si nanowire arrays. Detailed structural analysis reveals that compared to the other two types, the orthorhombic NiSe₂ NCs are more metallic and form less surface oxides. As a result, the orthorhombic NiSe₂ NCs significantly enhanced the performance of water-splitting PEC cells by increasing the photocurrents and shifting the onset potentials. The high photocurrent is ascribed to the excellent catalytic activity toward water splitting, resulting in a low charge-transfer resistance. The onset potential shift can be determined by the shift of the flat-band potential. A large band bending occurs at the electrolyte interface, so that photoelectrons or photoholes are efficiently generated to accelerate the photocatalytic reaction at the active sites of orthorhombic NiSe₂. The remarkable bifunctional photocatalytic activity of orthorhombic NiSe₂ promises efficient PEC water splitting.

Highly Dispersive MoP Nanoparticles Anchored on Reduced Graphene Oxide Nanosheets for an Efficient Hydrogen Evolution Reaction Electrocatalyst

Electrochemical water-splitting with non-noble metal catalysts provides an eco-friendly strategy for renewable production of hydrogen. In this study, the MoP@C@reduced graphene oxide (rGO) composite was prepared via mild reactions through a chemical bath and postannealing process. With the assistance of citric acid, the MoP@C@rGO composite containing ultrafine MoP nanoparticles with a size of 3 nm anchored on two-dimensional C/rGO nanosheets has been obtained. The chelation effect with citric acid and the merits of rGO not only lead to affordable active sites but also improved the electrical conductivity and stability at the same time. Serving as the hydrogen evolution reaction (HER) electrocatalyst, the MoP@C@rGO composite presents a small overpotential of 168.9 mV at 10 mA cm^-2. It has superior durability when compared to samples of pure MoP, MoP@C, and MoP@rGO. The relative high activity and stable performance as well as the simple preparation process make the MoP@C@rGO composite a promising HER electrocatalyst.