The Role of Transition Metal Versus Coordination Mode in Single-Atom Catalyst for Electrocatalytic Sulfur Reduction Reaction.

Electrocatalytic sulfur reduction reaction (SRR) is emerging as an effective strategy to combat the polysulfide shuttling effect, which remains a critical factor impeding the practical application of the Li-S battery. Single-atom catalyst (SAC), one of the most studied catalytic materials, has shown considerable potential in addressing the polysulfide shuttling effect in a Li-S battery. However, the role played by transition metal vs coordination mode in electrocatalytic SRR is trial-and-error, and the general understanding that guides the synthesis of the specific SAC with desired property remains elusive. Herein, we use first-principles calculations and machine learning to screen a comprehensive data set of graphene-based SACs with different transition metals, heteroatom doping, and coordination modes. The results reveal that the type of transition metal plays the decisive role in SAC for electrocatalytic SRR, rather than the coordination mode. Specifically, the 3d transition metals exhibit admirable electrocatalytic SRR activity for all of the coordination modes. Compared with the reported N3C1 and N4 coordinated graphene-based SACs covering 3d, 4d, and 5d transition metals, the proposed para-MnO2C2 and para-FeN2C2 possess significant advantages on the electrocatalytic SRR, including a considerably low overpotential down to 1 mV and reduced Li2S decomposition energy barrier, both suggesting an accelerated conversion process among the polysulfides. This study may clarify some understanding of the role played by transition metal vs coordination mode for SAC materials with specific structure and desired catalytic properties toward electrocatalytic SRR and beyond.

Kirkendall effect-induced uniform stress distribution stabilizes nickel-rich layered oxide cathodes.

Nickel-rich layered oxide cathodes promise ultrahigh energy density but is plagued by the mechanical failure of the secondary particle upon (de)lithiation. Existing approaches for alleviating the structural degradation could retard pulverization, yet fail to tune the stress distribution and root out the formation of cracks. Herein, we report a unique strategy to uniformize the stress distribution in secondary particle via Kirkendall effect to stabilize the core region during electrochemical cycling. Exotic metal/metalloid oxides (such as Al2O3 or SiO2) is introduced as the heterogeneous nucleation seeds for the preferential growth of the precursor. The calcination treatment afterwards generates a dopant-rich interior structure with central Kirkendall void, due to the different diffusivity between the exotic element and nickel atom. The resulting cathode material exhibits superior structural and electrochemical reversibility, thus contributing to a high specific energy density (based on cathode) of 660 Wh kg-1 after 500 cycles with a retention rate of 86%. This study suggests that uniformizing stress distribution represents a promising pathway to tackle the structural instability facing nickel-rich layered oxide cathodes.

Establishing reaction networks in the 16-electron sulfur reduction reaction.

The sulfur reduction reaction (SRR) plays a central role in high-capacity lithium sulfur (Li-S) batteries. The SRR involves an intricate, 16-electron conversion process featuring multiple lithium polysulfide intermediates and reaction branches1-3. Establishing the complex reaction network is essential for rational tailoring of the SRR for improved Li-S batteries, but represents a daunting challenge4-6. Herein we systematically investigate the electrocatalytic SRR to decipher its network using the nitrogen, sulfur, dual-doped holey graphene framework as a model electrode to understand the role of electrocatalysts in acceleration of conversion kinetics. Combining cyclic voltammetry, in situ Raman spectroscopy and density functional theory calculations, we identify and directly profile the key intermediates (S8, Li2S8, Li2S6, Li2S4 and Li2S) at varying potentials and elucidate their conversion pathways. Li2S4 and Li2S6 were predominantly observed, in which Li2S4 represents the key electrochemical intermediate dictating the overall SRR kinetics. Li2S6, generated (consumed) through a comproportionation (disproportionation) reaction, does not directly participate in electrochemical reactions but significantly contributes to the polysulfide shuttling process. We found that the nitrogen, sulfur dual-doped holey graphene framework catalyst could help accelerate polysulfide conversion kinetics, leading to faster depletion of soluble lithium polysulfides at higher potential and hence mitigating the polysulfide shuttling effect and boosting output potential. These results highlight the electrocatalytic approach as a promising strategy for tackling the fundamental challenges regarding Li-S batteries.

Facile Electroless Plating Method to Fabricate a Nickel-Phosphorus-Modified Copper Current Collector for a Lean Lithium-Metal Anode.

The compatibility of current collectors with reactive Li is key to inducing stable Li cycling and prolonged cycle life of lean Li-metal batteries. Herein, a thin and uniform layer of Ni-P complex was built on the surface of a Cu current collector (NiP@Cu) via an efficient, controllable, and cost-effective electroless plating method. The thickness, morphology, composition, and roughness of the Ni-P deposition were successfully regulated. Lithiophilicity of the current collector was greatly improved by Ni-P deposition, which effectively reduced the Li nucleation overpotential and suppressed the Li dendrite growth. In addition, NiP@Cu promoted an inorganic LiF/Li3P-rich solid electrolyte interphase to facilitate interfacial charge transfer and eliminate excessive side reactions between Li and the electrolyte. As a result, the Coulombic efficiency of half-cells remained above 98.5% for more than 400 cycles at 0.5 mA/cm2 and 98.2% for more than 250 cycles at 1 mA/cm2. Full cells with NiP@Cu also showed superior performance compared to those with bare Cu. This work proposes a promising surface modification method to develop a stable, dendrite-free, and cost-effective anode current collector for high-energy-density lean Li-metal batteries.

Influencing Factors of International Students' Anxiety Under Online Learning During the COVID-19 Pandemic: A Cross-Sectional Study of 1,090 Chinese International Students.

Objective: We conducted the following cross-sectional study to comprehensively assess the anxiety among Chinese international students who studied online during the COVID-19 pandemic and its influencing factors. Methods: Questionnaires were distributed through "Sojump," and a total of 1,090 valid questionnaires were collected. The questionnaire was divided into two parts: general situation and anxiety assessment of students. The former used a self-made questionnaire, and the international general GAD-7 scale was used to measure anxiety. Chi-square test was used to analyze the differences between groups, and logistic regression analysis was performed for the factors with differences. Results: Anxiety was found in 707 (64.9%) of 1,090 international students. Chi-square test and multivariate Logistic regression analysis showed that the incidence of anxiety was higher in the group under 22 years of age than in the group over 22 years of age (68% vs. 61%, p = 0.015; OR = 1.186, 95% CI 1.045-1.347, p = 0.008); International students living in big cities had a higher incidence of anxiety than those living in rural areas (67% vs. 60%, p = 0.022; OR = 1.419, 95%CI 1.038-1.859, p = 0.011); international students who socialized 3 times or less monthly had a higher incidence of anxiety than those who socialized more than 3 times per month (68% vs. 58%, p = 0.003; OR = 1.52, 95%CI 1.160-1.992, p = 0.002); international students who expected purely online teaching had a higher incidence of anxiety than those who expected purely offline teaching or dual-track teaching (72% vs. 64%, p = 0.037; OR = 1.525, 95%CI 1.069-2.177, p = 0.02); international students with a subjective score of online learning experience of 6 or less had a higher incidence of anxiety than those with subjective scores of more than 6 (70% vs. 60%, p = 0.001, OR = 1.25, 95%CI 1.099-1.422, p = 0.001). However, gender, emotional status, BMI, major of study, vaccination status, and degree type had no significant difference in the incidence of anxiety among international students who studied online during the COVID-19 pandemic. Conclusion: During COVID-19, international students who were younger, came from big cities, had low social frequency, expected purely online teaching, and had poor experience of online classes were risk factors for anxiety during online classes.

The promises, challenges and pathways to room-temperature sodium-sulfur batteries.

Room-temperature sodium-sulfur batteries (RT-Na-S batteries) are attractive for large-scale energy storage applications owing to their high storage capacity as well as the rich abundance and low cost of the materials. Unfortunately, their practical application is hampered by severe challenges, such as low conductivity of sulfur and its reduced products, volume expansion, polysulfide shuttling effect and Na dendrite formation, which can lead to rapid capacity fading. The review discusses the Na-S-energy-storage chemistry, highlighting its promise, key challenges and potential strategies for large-scale energy storage systems. Specifically, we review the electrochemical principles and the current technical challenges of RT-Na-S batteries, and discuss the strategies to address these obstacles. In particular, we give a comprehensive review of recent progresses in cathodes, anodes, electrolytes, separators and cell configurations, and provide a forward-looking perspective on strategies toward robust high-energy-density RT-Na-S batteries.

A Silicon Monoxide Lithium-Ion Battery Anode with Ultrahigh Areal Capacity.

Silicon monoxide (SiO) is an attractive anode material for next-generation lithium-ion batteries for its ultra-high theoretical capacity of 2680 mAh g-1. The studies to date have been limited to electrodes with a relatively low mass loading (< 3.5 mg cm-2), which has seriously restricted the areal capacity and its potential in practical devices. Maximizing areal capacity with such high-capacity materials is critical for capitalizing their potential in practical technologies. Herein, we report a monolithic three-dimensional (3D) large-sheet holey graphene framework/SiO (LHGF/SiO) composite for high-mass-loading electrode. By specifically using large-sheet holey graphene building blocks, we construct LHGF with super-elasticity and exceptional mechanical robustness, which is essential for accommodating the large volume change of SiO and ensuring the structure integrity even at ultrahigh mass loading. Additionally, the 3D porous graphene network structure in LHGF ensures excellent electron and ion transport. By systematically tailoring microstructure design, we show the LHGF/SiO anode with a mass loading of 44 mg cm-2 delivers a high areal capacity of 35.4 mAh cm-2 at a current of 8.8 mA cm-2 and retains a capacity of 10.6 mAh cm-2 at 17.6 mA cm-2, greatly exceeding those of the state-of-the-art commercial or research devices. Furthermore, we show an LHGF/SiO anode with an ultra-high mass loading of 94 mg cm-2 delivers an unprecedented areal capacity up to 140.8 mAh cm-2. The achievement of such high areal capacities marks a critical step toward realizing the full potential of high-capacity alloy-type electrode materials in practical lithium-ion batteries.

Silver nanoparticles boost charge-extraction efficiency in Shewanella microbial fuel cells.

Microbial fuel cells (MFCs) can directly convert the chemical energy stored in organic matter to electricity and are of considerable interest for power generation and wastewater treatment. However, the current MFCs typically exhibit unsatisfactorily low power densities that are largely limited by the sluggish transmembrane and extracellular electron-transfer processes. Here, we report a rational strategy to boost the charge-extraction efficiency in Shewanella MFCs substantially by introducing transmembrane and outer-membrane silver nanoparticles. The resulting Shewanella-silver MFCs deliver a maximum current density of 3.85 milliamperes per square centimeter, power density of 0.66 milliwatts per square centimeter, and single-cell turnover frequency of 8.6 × 105 per second, which are all considerably higher than those of the best MFCs reported to date. Additionally, the hybrid MFCs feature an excellent fuel-utilization efficiency, with a coulombic efficiency of 81%.

Bacteria-Derived Biological Carbon Building Robust Li-S Batteries.

Lithium sulfur (Li-S) batteries are attracting increasing interest for high-density energy storage. However, the practical application is limited by the rapid capacity fading over repeated charge/discharge cycles which is largely attributed to the formation and shuttling of soluble polysulfide species. To address these issues, we develop a hierarchical structure composite with triple protection strategy via graphene, organic conductor PEDOT, and nitrogen and phosphorus codoped biological carbon to encapsulate sulfur species (GOC@NPBCS). This unique hierarchical structure can effectively immobilize the sulfur species while at the same time improve the electrical conductivity and ensure efficient lithium ion transport to enable excellent Li-S battery performance. In particular, the biological carbon derived from natural bacteria features inherent nitrogen and phosphorus codoping with a strong absorption to lithium polysulfides, which can greatly suppress the dissolution and shuttling of polysulfides that are responsible for rapid capacity fading. With these synergistic effects, the GOC@NPBCS cathode exhibits exceptionally stable cycling stability (an ultralow capacity fading rate of 0.045% per cycle during 1000 cycles at the current rate of 5 C), high specific capacity (1193.8 mAh g-1 at 0.5 C based on sulfur weight), and excellent rate capability.

Double-negative-index ceramic aerogels for thermal superinsulation.

Ceramic aerogels are attractive for thermal insulation but plagued by poor mechanical stability and degradation under thermal shock. In this study, we designed and synthesized hyperbolic architectured ceramic aerogels with nanolayered double-pane walls with a negative Poisson's ratio (-0.25) and a negative linear thermal expansion coefficient (-1.8 × 10-6 per °C). Our aerogels display robust mechanical and thermal stability and feature ultralow densities down to ~0.1 milligram per cubic centimeter, superelasticity up to 95%, and near-zero strength loss after sharp thermal shocks (275°C per second) or intense thermal stress at 1400°C, as well as ultralow thermal conductivity in vacuum [~2.4 milliwatts per meter-kelvin (mW/m·K)] and in air (~20 mW/m·K). This robust material system is ideal for thermal superinsulation under extreme conditions, such as those encountered by spacecraft.

Size-dependent kinetics during non-equilibrium lithiation of nano-sized zinc ferrite.

Spinel transition metal oxides (TMOs) have emerged as promising anode materials for lithium-ion batteries. It has been shown that reducing their particle size to nanoscale dimensions benefits overall electrochemical performance. Here, we use in situ transmission electron microscopy to probe the lithiation behavior of spinel ZnFe2O4 as a function of particle size. We have found that ZnFe2O4 undergoes an intercalation-to-conversion reaction sequence, with the initial intercalation process being size dependent. Larger ZnFe2O4 particles (40 nm) follow a two-phase intercalation reaction. In contrast, a solid-solution transformation dominates the early stages of discharge when the particle size is about 6-9 nm. Using a thermodynamic analysis, we find that the size-dependent kinetics originate from the interfacial energy between the two phases. Furthermore, the conversion reaction in both large and small particles favors {111} planes and follows a core-shell reaction mode. These results elucidate the intrinsic mechanism that permits fast reaction kinetics in smaller nanoparticles.

Solvent-Dependent Intercalation and Molecular Configurations in Metallocene-Layered Crystal Superlattices.

Organic-inorganic superlattices are a class of artificial structures of significant scientific and technological importance. Forming these hybrid materials can be achieved via controlled intercalation of organic molecules into inorganic layered hosts, which is a complex course involving multiple physicochemical processes. In solution phase, it is further complicated by interaction of solvent molecules with the intercalant and/or host. Here we describe an intercalation system exhibiting strong solvent-dependent kinetics and phase evolution. In revisiting intercalation of ferrocene into layered VOPO4·2H2O material by taking into account the influence of solvent, we are able to unravel molecular configurations of ferrocene molecules. An exclusive orientation of ferrocene but different arrangements among the layers are concluded in two model solvents. Resolving this complicated structure is possible thanks to a combined experimental and theoretical approach. Our study provides new insights into understanding molecular configurations and controlling intercalation kinetics in creating organic-inorganic superlattices, which may offer unprecedented properties beyond conventional materials.

Data on photovoltaic system using different perturb and observe methods under fast multi-changing solar irradiances.

This article presents the data on photovoltaic (PV) system used different perturb and observe (P&O) methods under fast multi-changing solar irradiances. The mathematical modeling of the PV system and tangent error P&O method was discussed in our previous study entitled "A novel tangent error maximum power point tracking algorithm for photovoltaic system under fast multi-changing solar irradiances" by Peng et al. (2018) [1]. The data provided in this paper can be used directly without having to spend weeks to simulate the output performance. In addition, it is easy to apply the results for comparison with other algorithms (Kollimalla et al., 2014; Belkaid et al., 2016; Chenchen et al., 2015; Jubaer and Zainal, 2015) [2,3,4,5], and develop a new method for practical application.

Dual Tuning of Ni-Co-A (A = P, Se, O) Nanosheets by Anion Substitution and Holey Engineering for Efficient Hydrogen Evolution.

Seeking earth-abundant electrocatalysts with high efficiency and durability has become the frontier of energy conversion research. Mixed-transition-metal (MTM)-based electrocatalysts, owing to the desirable electrical conductivity, synergistic effect of bimetal atoms, and structural stability, have recently emerged as new-generation hydrogen evolution reaction (HER) electrocatalysts. However, the correlation between anion species and their intrinsic electrocatalytic properties in MTM-based electrocatalysts is still not well understood. Here we present a novel approach to tuning the anion-dependent electrocatalytic characteristics in MTM-based catalyst for HER, using holey Ni/Co-based phosphides/selenides/oxides (Ni-Co-A, A = P, Se, O) as the model materials. The electrochemical results, combined with the electrical conductivity measurement and DFT calculation, reveal that P substitution could modulate the electron configuration, lower the hydrogen adsorption energy, and facilitate the desorption of hydrogen on the active sites in Ni-Co-A holey nanostructures, resulting in superior HER catalytic activity. Accordingly we fabricate the NCP holey nanosheet electrocatalyst for HER with an ultralow onset overpotential of nearly zero, an overpotential of 58 mV, and long-term durability, along with an applied potential of 1.56 V to boost overall water splitting at 10 mA cm-2, among the best electrocatalysts reported for non-noble-metal catalysts to date. This work not only presents a deeper understanding of the intrinsic HER electrocatalytic properties for MTM-based electrocatalyst with various anion species but also offers new insights to better design efficient and durable water-splitting electrocatalysts.

Stretchable All-Gel-State Fiber-Shaped Supercapacitors Enabled by Macromolecularly Interconnected 3D Graphene/Nanostructured Conductive Polymer Hydrogels.

Nanostructured conductive polymer hydrogels (CPHs) have been extensively applied in energy storage owing to their advantageous features, such as excellent electrochemical activity and relatively high electrical conductivity, yet the fabrication of self-standing and flexible electrode-based CPHs is still hampered by their limited mechanical properties. Herein, macromolecularly interconnected 3D graphene/nanostructured CPH is synthesized via self-assembly of CPHs and graphene oxide macrostructures. The 3D hybrid hydrogel shows uniform interconnectivity and enhanced mechanical properties due to the strong macromolecular interaction between the CPHs and graphene, thus greatly reducing aggregation in the fiber-shaping process. A proof-of-concept all-gel-state fibrous supercapacitor based on the 3D polyaniline/graphene hydrogel is fabricated to demonstrate the outstanding flexibility and mouldability, as well as superior electrochemical properties enabled by this 3D hybrid hydrogel design. The proposed device can achieve a large strain (up to ≈40%), and deliver a remarkable volumetric energy density of 8.80 mWh cm-3 (at power density of 30.77 mW cm-3 ), outperforming many fiber-shaped supercapacitors reported previously. The all-hydrogel design opens up opportunities in the fabrication of next-generation wearable and portable electronics.

Structural Engineering of 2D Nanomaterials for Energy Storage and Catalysis.

Research on 2D nanomaterials is rising to an unprecedented height and will continue to remain a very important topic in materials science. In parallel with the discovery of new candidate materials and exploration of their unique characteristics, there are intensive interests to rationally control and tune the properties of 2D nanomaterials in a predictable manner. Considerable attention is focused on modifying these materials structurally or engineering them into designed architectures to meet requirements for specific applications. Recent advances in such structural engineering strategies have demonstrated their ability to overcome current material limitations, showing great promise for promoting device performance to a new level in many energy-related applications. Existing in many forms, these strategies can be categorized based on how they intrinsically or extrinsically alter the pristine structure. Achieved through various synthetic routes and practiced in a range of different material systems, they usually share common descriptors that predestine them to be effective in certain circumstances. Therefore, understanding the underlying mechanism of these strategies to provide fundamental insights into structural design and property tailoring is of critical importance. Here, the most recent development of structural engineering of 2D nanomaterials and their significant effects in energy storage and catalysis technologies are addressed.

Cyanogel-Enabled Homogeneous Sb-Ni-C Ternary Framework Electrodes for Enhanced Sodium Storage.

Antimony (Sb) represents an important high-capacity anode material for advanced sodium ion batteries, but its practical utilization has been primarily hampered by huge volume expansion-induced poor cycling life. The co-incorporation of transition-metal (M = Ni, Cu, Fe, etc.) and carbon components can synergistically buffer the volume change of the Sb component; however, these Sb-M-C ternary anodes often suffer from uneven distribution of Sb, M, and C components. Herein, we propose a general nanostructured gel-enabled methodology to synthesize homogeneous Sb-M-C ternary anodes for fully realizing the synergestic effects from M/C dual matrices. A cyano-bridged Sb(III)-Ni(II) coordination polymer gel (Sb-Ni cyanogel) has been synthesized and directly reduced to an Sb-Ni alloy framework (Sb-Ni framework). Moreover, graphene oxide (GO) can be in situ immobilized within the cyanogel framework, and after reduction, reduced graphene oxide (rGO) is uniformly distributed within the alloy framework, yielding a homogeneous rGO@Sb-Ni ternary framework. The rGO@Sb-Ni framework with optimal rGO content manifests a high reversible capacity of ∼468 mA h g-1 at 1 A g-1 and stable cycle life at 5 A g-1 (∼210 mA h g-1 after 500 cycles). The proposed cyanogel-enabled methodology may be extended to synthesize other homogeneous ternary framework materials for efficient energy storage and electrocatalysis.

Two-Dimensional Holey Nanoarchitectures Created by Confined Self-Assembly of Nanoparticles via Block Copolymers: From Synthesis to Energy Storage Property.

Advances in liquid-phase exfoliation and surfactant-directed anisotropic growth of two-dimensional (2D) nanosheets have enabled their rapid development. However, it remains challenging to develop assembly strategies that lead to the construction of 2D nanomaterials with well-defined geometry and functional nanoarchitectures that are tailored to specific applications. Here we report a facile self-assembly method leading to the controlled synthesis of 2D transition metal oxide (TMO) nanosheets containing a high density of holes. We utilize graphene oxide sheets as a sacrificial template and Pluronic copolymers as surfactants. By using ZnFe2O4 (ZFO) nanoparticles as a model material, we demonstrate that by tuning the molecular weight of the Pluronic copolymers we can incorporate the ZFO particles and tune the size of the holes in the sheets. The resulting 2D ZFO nanosheets offer synergistic characteristics including increased electrochemically active surface areas, shortened ion diffusion paths, and strong inherent mechanical properties, leading to enhanced lithium-ion storage properties. Postcycling characterization confirms that the samples maintain structural integrity after electrochemical cycling. Our findings demonstrate that this template-assisted self-assembly method is a useful bottom-up route for controlled synthesis of 2D nanoarchitectures, and these holey 2D nanoarchitectures are promising for improving the electrochemical performance of next-generation lithium-ion batteries.

Effective Interlayer Engineering of Two-Dimensional VOPO4 Nanosheets via Controlled Organic Intercalation for Improving Alkali Ion Storage.

Two-dimensional (2D) energy materials have shown the promising electrochemical characteristics for lithium ion storage. However, the decreased active surfaces and the sluggish charge/mass transport for beyond-lithium ion storage that has potential for large-scale energy storage systems, such as sodium or potassium ion storage, caused by the irreversible restacking of 2D materials during electrode processing remain a major challenge. Here we develop a general interlayer engineering strategy to address the above-mentioned challenges by using 2D ultrathin vanadyl phosphate (VOPO4) nanosheets as a model material for challenging sodium ion storage. Via controlled intercalation of organic molecules, such as triethylene glycol and tetrahydrofuran, the sodium ion transport in VOPO4 nanosheets has been significantly improved. In addition to advanced characterization including X-ray diffraction, high-resolution transmission electron microscopy, and X-ray absorption fine structure to characterize the interlayer and the chemical bonding/configuration between the organic intercalants and the VOPO4 host layers, density functional theory calculations are also performed to understand the diffusion behavior of sodium ions in the pure and TEG intercalated VOPO4 nanosheets. Because of the expanded interlayer spacing in combination with the decreased energy barriers for sodium ion diffusion, intercalated VOPO4 nanosheets show much improved sodium ion transport kinetics and greatly enhanced rate capability and cycling stability for sodium ion storage. Our results afford deeper understanding of the interlayer-engineering strategy to improve the sodium ion storage performance of the VOPO4 nanosheets. Our results may also shed light on possible multivalent-ion based energy storage such as Mg2+ and Al3+.

Metallic Transition Metal Selenide Holey Nanosheets for Efficient Oxygen Evolution Electrocatalysis.

Catalysts for oxygen evolution reaction (OER) are pivotal to the scalable storage of sustainable energy by means of converting water to oxygen and hydrogen fuel. Designing efficient electrocatalysis combining the features of excellent electrical conductivity, abundant active surface, and structural stability remains a critical challenge. Here, we report the rational design and controlled synthesis of metallic transition metal selenide NiCo2Se4-based holey nanosheets as a highly efficient and robust OER electrocatalyst. Benefiting from synergistic effects of metallic nature, heteroatom doping, and holey nanoarchitecture, NiCo2Se4 holey nanosheets exhibit greatly enhanced kinetics and improved cycling stability for OER. When further employed as an alkaline electrolyzer, the NiCo2Se4 holey nanosheet electrocatalyst enables a high-performing overall water splitting with a low applied external potential of 1.68 V at 10 mA cm-2. This work not only represents a promising strategy to design the efficient and robust OER catalysts but also provides fundamental insights into the structure-property-performance relationship of transition metal selenide-based electrocatalytic materials.