Synergism of Geometric Construction and Electronic Regulation: 3D Se‐(NiCo)Sx/(OH)x Nanosheets for Highly Efficient Overall Water Splitting

The exploration of highly efficient electrocatalysts for both oxygen and hydrogen generation via water splitting is receiving considerable attention in recent decades. Up till now, Pt‐based catalysts still exhibit the best hydrogen evolution reaction (HER) performance and Ir/Ru‐based oxides are identified as the benchmark for oxygen evolution reaction (OER). However, the high cost and rarity of these materials extremely hinder their large‐scale applications. This paper describes the construction of the ultrathin defect‐enriched 3D Se‐(NiCo)S_x/(OH)_x nanosheets for overall water splitting through a facile Se‐induced hydrothermal treatment. Via Se‐induced fabrication, highly efficient Se‐(NiCo)S_x/(OH)_x nanosheets are successfully fabricated through morphology optimization, defect engineering, and electronic structure tailoring. The as‐prepared hybrids exhibit relatively low overpotentials of 155 and 103 mV at the current density of 10 mA cm^?2 for OER and HER, respectively. Moreover, an overall water‐splitting device delivers a current density of 10 mA cm^?2 for ≈66 h without obvious degradation.     

Porous Cobalt–Nickel Hydroxide Nanosheets with Active Cobalt Ions for Overall Water Splitting

Low‐cost and high‐performance catalysts are of great significance for electrochemical water splitting. Here, it is reported that a laser‐synthesized catalyst, porous Co_0.75Ni_0.25(OH)₂ nanosheets, is highly active for catalyzing overall water splitting. The porous nanosheets exhibit low overpotentials for hydrogen evolution reaction (95 mV@10 mA cm^?2) and oxygen evolution reaction (235 mV@10 mA cm^?2). As both anode and cathode catalysts, the porous nanosheets achieve a current density of 10 mA cm^?2 at an external voltage of 1.56 V, which is much lower than that of commercial Ir/C‐Pt/C couple (1.62 V). Experimental and theoretical investigations reveal that numerous Co³⁺ ions are generated on the pore wall of nanosheets, and the unique atomic structure around Co³⁺ ions leads to appropriate electronic structure and adsorption energy of intermediates, thus accelerating hydrogen and oxygen evolution.     

Cobalt Iron Hydroxide as a Precious Metal‐Free Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Highly efficient and stable electrocatalysts from inexpensive and earth‐abundant elements are emerging materials in the overall water splitting process. Herein, cobalt iron hydroxide nanosheets are directly deposited on nickel foam by a simple and rapid electrodeposition method. The cobalt iron hydroxide (CoFe/NF) nanosheets not only allow good exposure of the highly active surface area but also facilitate the mass and charge transport capability. As an anode, the CoFe/NF electrocatalyst displays excellent oxygen evolution reaction catalytic activity with an overpotential of 220 mV at a current density of 10 mA cm^?2. As a cathode, it exhibits good performance in the hydrogen evolution reaction with an overpotential of 110 mV, reaching a current density of 10 mA cm^?2. When CoFe/NF electrodes are used as the anode and the cathode for water splitting, a low cell voltage of 1.64 V at 10 mA cm^?2 and excellent stability for 50 h are observed. The present work demonstrates a possible pathway to develop a highly active and durable substitute for noble metal electrocatalysts for overall water splitting.     

A Cost‐Efficient Bifunctional Ultrathin Nanosheets Array for Electrochemical Overall Water Splitting

The design of cost‐efficient earth‐abundant catalysts with superior performance for the electrochemical water splitting is highly desirable. Herein, a general strategy for fabricating superior bifunctional water splitting electrodes is reported, where cost‐efficient earth‐abundant ultrathin Ni‐based nanosheets arrays are directly grown on nickel foam (NF). The newly created Ni‐based nanosheets@NF exhibit unique features of ultrathin building block, 3D hierarchical structure, and alloy effect with the optimized Ni₅Fe layered double hydroxide@NF (Ni₅Fe LDH@NF) exhibiting low overpotentials of 210 and 133 mV toward both oxygen evolution reaction and hydrogen evolution reaction at 10 mA cm^?2 in alkaline condition, respectively. More significantly, when applying as the bifunctional overall water splitting electrocatalyst, the Ni₅Fe LDH@NF shows an appealing potential of 1.59 V at 10 mA cm^?2 and also superior durability at the very high current density of 50 mA cm^?2.     

Single Ni Atoms and Clusters Embedded in N‐Doped Carbon “Tubes on Fibers” Matrix with Bifunctional Activity for Water Splitting at High Current Densities

Among the bifunctional catalysts for water splitting, recently emerged transition‐metal single‐atom catalysts are theoretically considered to possess high potential, while the experimental activity is not satisfactory yet. Herein, an exceptionally efficient trifunctional metal–nitrogen–carbon (M–N–C) catalyst electrode, composed of a hierarchical carbon matrix embedding isolated nickel atoms with nickel–iron (NiFe) clusters, is presented. 1D microfibers and nanotubes grow sequentially from 2D nanosheets as sacrificial templates via two stages of solution‐ and solid‐phase reactions to form a 1D hierarchy. Exceptionally efficient bifunctional activity with an overpotential of only 13 mV at 10 mA cm^?2 toward hydrogen evolution reaction (HER) and an overpotential of 210 mV at 30 mA cm^?2 toward oxygen evolution reaction (OER) is obtained, surpassing each monofunctional activity ever reported. More importantly, an overpotential of only 126 and 326 mV is required to drive 500 mA cm^?2 toward the HER and OER, respectively. For the first time, industrial‐scale water splitting with two bifunctional catalyst electrodes with a current density of 500 mA cm^?2 at a potential of 1.71 V is demonstrated. Lastly, trifunctional catalytic activity including oxygen reduction reaction is also proven with a half‐wave potential at 0.848 V.     

Cobalt Covalent Doping in MoS2 to Induce Bifunctionality of Overall Water Splitting

The layer‐structured MoS₂ is a typical hydrogen evolution reaction (HER) electrocatalyst but it possesses poor activity for the oxygen evolution reaction (OER). In this work, a cobalt covalent doping approach capable of inducing HER and OER bifunctionality into MoS₂ for efficient overall water splitting is reported. The results demonstrate that covalently doping cobalt into MoS₂ can lead to dramatically enhanced HER activity while simultaneously inducing remarkable OER activity. The catalyst with optimal cobalt doping density can readily achieve HER and OER onset potentials of ?0.02 and 1.45 V (vs reversible hydrogen electrode (RHE)) in 1.0 m KOH. Importantly, it can deliver high current densities of 10, 100, and 200 mA cm^?2 at low HER and OER overpotentials of 48, 132, 165 mV and 260, 350, 390 mV, respectively. The reported catalyst activation approach can be adapted for bifunctionalization of other transition metal dichalcogenides.     

Surface Engineering of MoS2 via Laser‐Induced Exfoliation in Protic Solvents

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS₂) is considered a promising nonprecious candidate to substitute Pt‐based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one‐step exfoliation of bulk 2H‐MoS₂ to ultrastable few‐layer MoS₂ nanosheets. Such prepared MoS₂ nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H‐to‐1T phase transition under laser irradiation. MoS₂ exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm^?2 and Tafel slope of 54 mV dec^?1.     

An Efficient Cobalt Phosphide Electrocatalyst Derived from Cobalt Phosphonate Complex for All‐pH Hydrogen Evolution Reaction and Overall Water Splitting in Alkaline Solution

The development of low‐cost and highly efficient electrocatalysts via an eco‐friendly synthetic method is of great significance for future renewable energy storage and conversion systems. Herein, cobalt phosphides confined in porous P‐doped carbon materials (Co‐P@PC) are fabricated by calcinating the cobalt‐phosphonate complex formed between 1‐hydroxyethylidenediphosphonic acid and Co(NO₃)₂ in alkaline solution. The P‐containing ligand in the complex acts as the carbon source as well as in situ phosphorizing agent for the formation of cobalt phosphides and doping P element into carbon material upon calcination. The Co‐P@PC exhibits high activity for all‐pH hydrogen evolution reaction (overpotentials of 72, 85, and 76 mV in acidic, neutral, and alkaline solutions at the current density of 10 mA cm^?2) and oxygen evolution reaction in alkaline solution (an overpotential of 280 mV at the current density of 10 mA cm^?2). The alkaline electrolyzer assembled from the Co‐P@PC electrodes delivers the current density of 10 mA cm^?2 at the voltage of 1.60 V with a durability of 60 h. The excellent activity and long‐term stability of the Co‐P@PC derives from the synergistic effect between the active cobalt phosphides and the porous P‐doped carbon matrix.     

Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

To achieve excellent photoelectrochemical water‐splitting activity, photoanode materials with high light absorption and good charge‐separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO₃ (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen‐vacancy concentration (8.7%) exhibits high light‐absorption and good charge‐separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm^?2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm^?2 and stable gas production with an average solar‐to‐hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water‐splitting system.     

Exceptional Performance of Hierarchical Ni–Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting

Developing low‐cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth‐abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni–Fe layered‐double‐hydroxide (Ni–Fe LDH) nanosheets or porous Ni–Fe oxides (NiFeO_x) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as‐prepared Ni–Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm^?2 at an overpotential of 218 mV, which is smaller than that of RuO₂ catalyst (249 mV). In contrast, the resulting NiFeO_x@NiCu exhibits better HER activity, yielding a current density of 10 mA cm^?2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide‐based electrocatalysts. The remarkable activity of the Ni–Fe LDH@NiCu and NiFeO_x@NiCu is further demonstrated by a 1.5 V solar‐panel‐powered electrolyzer, resulting in current densities of 10 and 50 mA cm^?2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as‐prepared materials as the best bifunctional electrocatalysts so far.     

Phosphorus‐Rich Colloidal Cobalt Diphosphide (CoP2) Nanocrystals for Electrochemical and Photoelectrochemical Hydrogen Evolution

Developing earth‐abundant and efficient electrocatalysts for photoelectrochemical water splitting is critical to realizing a high‐performance solar‐to‐hydrogen energy conversion process. Herein, phosphorus‐rich colloidal cobalt diphosphide nanocrystals (CoP₂ NCs) are synthesized via hot injection. The CoP₂ NCs show a Pt‐like hydrogen evolution reaction (HER) electrocatalytic activity in acidic solution with a small overpotential of 39 mV to achieve ?10 mA cm^?2 and a very low Tafel slope of 32 mV dec^?1. Density functional theory (DFT) calculations reveal that the high P content both physically separates Co atoms to prevent H from over binding to multiple Co atoms, while simultaneously stabilizing H adsorbed to single Co atoms. The catalytic performance of the CoP₂ NCs is further demonstrated in a metal–insulator–semiconductor photoelectrochemical device consisting of bottom p‐Si light absorber, atomic layer deposition Al–ZnO passivation layers, and the CoP₂ cocatalyst. The p‐Si/AZO/TiO₂/CoP₂ photocathode shows a photocurrent density of ?16.7 mA cm^?2 at 0 V versus reversible hydrogen electrode (RHE) and an output photovoltage of 0.54 V. The high performance and stability are attributed to the junction between p‐Si and AZO, the corrosion‐resistance of the pinhole‐free TiO₂ protective layer, and the fast HER kinetics of the CoP₂ NCs.     

Highly Robust Non‐Noble Alkaline Hydrogen‐Evolving Electrocatalyst from Se‐Doped Molybdenum Disulfide Particles on Interwoven CoSe2 Nanowire Arrays

Developing efficient non‐noble and earth‐abundant hydrogen‐evolving electrocatalysts is highly desirable for improving the energy efficiency of water splitting in base. Molybdenum disulfide (MoS₂) is a promising candidate, but its catalytic activity is kinetically retarded in alkaline media due to the unfavorable water adsorption and dissociation feature. A heterogeneous electrocatalyst is reported that is constructed by selenium‐doped MoS₂ (Se‐MoS₂) particles on 3D interwoven cobalt diselenide (CoSe₂) nanowire arrays that drives the hydrogen evolution reaction (HER) with fast reaction kinetics in base. The resultant Se‐MoS₂/CoSe₂ hybrid exhibits an outstanding catalytic HER performance with extremely low overpotentials of 30 and 93 mV at 10 and 100 mA cm^–2 in base, respectively, which outperforms most of the inexpensive alkaline HER catalysts, and is among the best alkaline catalytic activity reported so far. Moreover, this hybrid catalyst shows exceptional catalytic performance with very low overpotentials of 84 and 95 mV at 10 mA cm^–2 in acidic and neutral electrolytes, respectively, implying robust pH universality of this hybrid catalyst. This work may provide new inspirations for the development of high‐performance MoS₂‐based HER electrocatalysts in unfavorable basic media for promising catalytic applications.     

Engineering of Electronic States on Co3O4 Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction

Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O‐vacancies (V_o) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution reduction (OER) performance on Co₃O₄ ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen‐deficient Fe‐Co‐O nanosheets (3–4 nm thickness) display an overpotential of 260 mV@10 mA cm^?2 and a Tafel slope of 53 mV dec^?1, outperforming those of the benchmark RuO₂ in 1.0 m KOH. Further calculations demonstrate that the combined introduction of Fe cation and V_o with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate‐limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen‐deficient Ni‐Co‐O nanosheets. This work not only establishes a clear atomic‐level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.     

FeS2/CoS2 Interface Nanosheets as Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Electrochemical water splitting to produce hydrogen and oxygen, as an important reaction for renewable energy storage, needs highly efficient and stable catalysts. Herein, FeS₂/CoS₂ interface nanosheets (NSs) as efficient bifunctional electrocatalysts for overall water splitting are reported. The thickness and interface disordered structure with rich defects of FeS₂/CoS₂ NSs are confirmed by atomic force microscopy and high‐resolution transmission electron microscopy. Furthermore, extended X‐ray absorption fine structure spectroscopy clarifies that FeS₂/CoS₂ NSs with sulfur vacancies, which can further increase electrocatalytic performance. Benefiting from the interface nanosheets' structure with abundant defects, the FeS₂/CoS₂ NSs show remarkable hydrogen evolution reaction (HER) performance with a low overpotential of 78.2 mV at 10 mA cm⁻² and a superior stability for 80 h in 1.0 m KOH, and an overpotential of 302 mV at 100 mA cm⁻² for the oxygen evolution reaction (OER). More importantly, the FeS₂/CoS₂ NSs display excellent performance for overall water splitting with a voltage of 1.47 V to achieve current density of 10 mA cm⁻² and maintain the activity for at least 21 h. The present work highlights the importance of engineering interface nanosheets with rich defects based on transition metal dichalcogenides for boosting the HER and OER performance.     

Hybridization of Defective Tin Disulfide Nanosheets and Silver Nanowires Enables Efficient Electrochemical Reduction of CO2 into Formate and Syngas

Integrating the defect engineering and conductivity promotion represents a promising way to improve the performance of CO₂ electrochemical reduction. Herein, the hybridized composite of defective SnS₂ nanosheets and Ag nanowires is developed as an efficient catalyst for the production of formate and syngas toward CO₂ electrochemical reduction. The Schottky barrier in Ag‐SnS₂ hybrid nanosheets is negligible due to the similar Fermi level of SnS₂ nanosheets and Ag nanowires. Accordingly, the free electrons of Ag nanowires participate in the electronic transport of SnS₂ nanosheets, and thus give rise to a 5.5‐fold larger carrier density of Ag‐SnS₂ hybrid nanosheets than that of SnS₂ nanosheets. In CO₂ electrochemical reduction, the Ag‐SnS₂ hybrid nanosheets display 38.8 mA cm^?2 of geometrical current density at –1.0 V vs reversible hydrogen electrode, including 23.3 mA cm^?2 for formate and 15.5 mA cm^?2 for syngas with the CO/H₂ ratio of 1:1. A mechanistic study reveals that the abundant defect sites and carrier density not only promote the conductivity of the electrocatalyst, but also increase the binding strength for CO₂, which account for the efficient CO₂ reduction.     

Highly Efficient Hydrogen Evolution from a Mesoporous Hybrid of Nickel Phosphide Nanoparticles Anchored on Cobalt Phosphosulfide/Phosphide Nanosheet Arrays

Facile design of low‐cost and high‐efficiency catalysts with earth‐abundant and cheap materials is desirable to replace platinum (Pt) for the hydrogen evolution reaction (HER) in water splitting, but the development of such HER catalysts with Pt‐like activity using simple strategies remains challenging. A mesoporous hybrid catalyst of nickel phosphides nanoparticles and cobalt phosphosulfide/phosphide (CoS|Ni|P) nanosheet arrays for HER is reported here, which is developed by a facile three‐step approach consisting of electrodeposition, thermal sulfurization, and phosphorization. This hybrid catalyst is highly robust and stable in acid for HER, and is distinguished by very low overpotentials of 41, 88, and 150 mV to achieve 10, 100, and 1000 mA cm^?2, respectively, as well as a small Tafel slope (45.2 mV dec^?1), and a large exchange current density (964 µA cm^?2). It is among the most efficient earth‐abundant catalysts reported thus far for HER. More importantly, this electrocatalyst has electrochemical durability over 20 h under a wide range of current densities (up to 1 A cm^?2) in acidic conditions, as well as very high turnover frequencies of 0.40 and 1.26 H₂ s^?1 at overpotentials of 75 and 100 mV, respectively, showing that it has great potential for practical applications in large‐scale water electrolysis.     

Nickel@Nitrogen‐Doped Carbon@MoS2 Nanosheets: An Efficient Electrocatalyst for Hydrogen Evolution Reaction

Developing cheap, abundant, and easily available electrocatalysts to drive the hydrogen evolution reaction (HER) at small overpotentials is an urgent demand of hydrogen production from water splitting. Molybdenum disulfide (MoS₂) based composites have emerged as competitive electrocatalysts for HER in recent years. Herein, nickel@nitrogen‐doped carbon@MoS₂ nanosheets (Ni@NC@MoS₂) hybrid sub‐microspheres are presented as HER catalyst. MoS₂ nanosheets with expanded interlayer spacings are vertically grown on nickel@nitrogen‐doped carbon (Ni@NC) substrate to form Ni@NC@MoS₂ hierarchical sub‐microspheres by a simple hydrothermal process. The formed Ni@NC@MoS₂ composites display excellent electrocatalytic activity for HER with an onset overpotential of 18 mV, a low overpotential of 82 mV at 10 mA cm^?2, a small Tafel slope of 47.5 mV dec^?1, and high durability in 0.5 H₂SO₄ solution. The outstanding HER performance of the Ni@NC@MoS₂ catalyst can be ascribed to the synergistic effect of dense catalytic sites on MoS₂ nanosheets with exposed edges and expanded interlayer spacings, and the rapid electron transfer from Ni@NC substrate to MoS₂ nanosheets. The excellent Ni@NC@MoS₂ electrocatalyst promises potential application in practical hydrogen production, and the strategy reported here can also be extended to grow MoS₂ on other nitrogen‐doped carbon encapsulated metal species for various applications.     

A Robust Nonprecious CuFe Composite as a Highly Efficient Bifunctional Catalyst for Overall Electrochemical Water Splitting

To generate hydrogen, which is a clean energy carrier, a combination of electrolysis and renewable energy sources is desirable. In particular, for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrolysis, it is necessary to develop nonprecious, efficient, and durable catalysts. A robust nonprecious copper–iron (CuFe) bimetallic composite is reported that can be used as a highly efficient bifunctional catalyst for overall water splitting in an alkaline medium. The catalyst exhibits outstanding OER and HER activity, and very low OER and HER overpotentials (218 and 158 mV, respectively) are necessary to attain a current density of 10 mA cm^?2. When used in a two‐electrode water electrolyzer system for overall water splitting, it not only achieves high durability (even at a very high current density of 100 mA cm^?2) but also reduces the potential required to split water into oxygen and hydrogen at 10 mA cm^?2 to 1.64 V for 100 h of continuous operation.     

Strong Electronic Interaction in Dual‐Cation‐Incorporated NiSe2 Nanosheets with Lattice Distortion for Highly Efficient Overall Water Splitting

Exploring highly efficient and low‐cost electrocatalysts for electrochemical water splitting is of importance for the conversion of intermediate energy. Herein, the synthesis of dual‐cation (Fe, Co)‐incorporated NiSe₂ nanosheets (Fe, Co‐NiSe₂) and systematical investigation of their electrocatalytic performance for water splitting as a function of the composition are reported. The dual‐cation incorporation can distort the lattice and induce stronger electronic interaction, leading to increased active site exposure and optimized adsorption energy of reaction intermediates compared to single‐cation‐doped or pure NiSe₂. As a result, the obtained Fe_0.09Co_0.13‐NiSe₂ porous nanosheet electrode shows an optimized catalytic activity with a low overpotential of 251 mV for oxygen evolution reaction and 92 mV for hydrogen evolution reaction (both at 10 mA cm^?2 in 1 m KOH). When used as bifunctional electrodes for overall water splitting, the current density of 10 mA cm^?2 is achieved at a low cell voltage of 1.52 V. This work highlights the importance of dual‐cation doping in enhancing the electrocatalyst performance of transition metal dichalcogenides.     

Construction of Defect‐Rich Ni‐Fe‐Doped K0.23MnO2 Cubic Nanoflowers via Etching Prussian Blue Analogue for Efficient Overall Water Splitting

Designing elaborate nanostructures and engineering defects have been promising approaches to fabricate cost‐efficient electrocatalysts toward overall water splitting. In this work, a controllable Prussian‐blue‐analogue‐sacrificed strategy followed by an annealing process to harvest defect‐rich Ni‐Fe‐doped K_0.23MnO₂ cubic nanoflowers (Ni‐Fe‐K_0.23MnO₂ CNFs‐300) as highly active bifunctional catalysts for oxygen and hydrogen evolution reactions (OER and HER) is reported. Benefiting from many merits, including unique morphology, abundant defects, and doping effect, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 shows the best electrocatalytic performances among currently reported Mn oxide‐based electrocatalysts. This catalyst affords low overpotentials of 270 (320) mV at 10 (100) mA cm^?2 for OER with a small Tafel slope of 42.3 mV dec^?1, while requiring overpotentials of 116 and 243 mV to attain 10 and 100 mA cm^?2 for HER respectively. Moreover, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 applied to overall water splitting exhibits a low cell voltage of 1.62 V at 10 mA cm^?2 and excellent durability, even superior to the Pt/C||IrO₂ cell at large current density. Density functional theory calculations further confirm that doping Ni and Fe into the crystal lattice of δ‐MnO₂ can not only reinforce the conductivity but also reduces the adsorption free‐energy barriers on the active sites during OER and HER.