First insight on Mo(II) as electrocatalytically active species for oxygen evolution reaction

The replacement of noble metals with earth-abundant metals is still a big challenge for the practical application of electrocatalysis. In this work, we have developed the Mo_xC-modified alloy@nitrogen-doped carbon hybrid electrocatalysts (Mo_xC-alloy@NC, alloy: FeCo, NiCo) for oxygen evolution reaction (OER) by a simple thermolysis method. Compared with FeCo@NC and NiCo@NC, the OER performances of Mo_xC-FeCo@NC and MoC-NiCo@NC are greatly enhanced, mainly due to the improved electrical conductivity by the introduce of Mo_xC. Moreover, Mo_xC-FeCo@NC exhibits a smaller Tafel slope (80 mV/dec) and a lower overpotential (318 mV) at 10 mA cm⁻² in 1 M KOH solution, compared with MoC-NiCo@NC (186 mV/dec, 352 mV). In consideration of a lower BET area (6.6 m² g⁻¹) of Mo_xC-FeCo@NC than those of MoC-NiCo@NC (25.4 m² g⁻²), the remarkable electrocatalytic activity of Mo_xC-FeCo@NC is mainly attributed to the presence of Mo(II) acting as the OER active species. Although Mo as hydrogen evolution reaction (HER) active species is well known, Mo(II) as the OER active species has not been reported before.     

Enriched oxygen vacancy promoted heteroatoms (B,P, N,and S) doped CeO2: Challenging electrocatalysts for oxygen evolution reaction (OER) in alkaline medium

Increasing worldwide energy consumption has prompted considerable study into energy generation and energy storage systems in recent years. Chemical fuels may be produced efficiently via electrocatalytic water splitting, which uses electric and solar power. The development of efficient anodic electrocatalysts for efficient oxygen evolution reaction (OER) is a greater concern of present energy research. Cerium oxide (CeO₂) are promising electrocatalysts that exhibit outstanding OER but their reduced stability obstructs the practical application. A novel strategy was established to construct an effective catalyst of heteroatom (N, B, P and S) doped CeO₂ matrix were prepared. Moreover, the doping of heteroatoms into the CeO₂ matrix processes the improved electronic conductivity, reactive sites, increases the electrochemical catalytic activity, which enhances the water oxidation reaction. Consequently, well-suited alkaline electrolysers were brought together for water oxidation to ideal OER electrocatalytic activity. The OER activity of the electrocatalysts follows the order of S–CeO₂ (190 mV@10 mA cm⁻²), N– CeO₂ (220 mV @10 mA cm⁻²), P– CeO₂ (230 mV @10 mA cm⁻²), B–CeO₂ (250 mV @10 mA cm⁻²) and CeO₂ (260 mV @10 mA cm⁻²) in 1 M of KOH. From the kinetics analysis, Tafel slope value achieved for catalysts CeO₂, B–CeO_2, P–CeO₂, N–CeO₂ and S–CeO₂ are 142 mV dec⁻¹,121 mV dec⁻¹, 102 mV dec⁻¹, 98 mV dec⁻¹ and 83 mV dec⁻¹ respectively. These results validate that the S–CeO₂ electrode is prominent for OER performance with the requirement of cell voltage of 1.42 V at 10 mA cm⁻² current density. In addition, sulphur doped CeO₂ relatively have excellent stability through chrono-potentiometric analysis lasting for 20 h. Although the heteroatoms doped CeO₂ is acts as anode material, the preparation method is widespread, which will reduce the synthesis cost and streamline the preparation of electrode for OER. This research effort delivers a complete advantage for the development of robust, environmentally friendly and highly dynamic electrocatalysts for OER activity.     

Accelerated oxygen evolution kinetics on NiFeAl-layered double hydroxide electrocatalysts with defect sites prepared by electrodeposition

NiFe layered double hydroxides (LDHs) is considered to be one of the LDHs electrocatalyst materials with the best electrocatalytic oxygen evolution properties. However, its poor conductivity and inherently poor electrocatalytic activity are considered to be the limiting factors inhibiting the electrocatalytic properties for oxygen evolution reaction (OER). The amorphous NiFeAl-LDHs electrocatalysts were prepared by electrodeposition with nickel foam as the support, and the D-NiFeAl-LDHs electrocatalyst with defect sites was then obtained by alkali etching. The mechanism of catalysts with defect sites in OER was analyzed. The ingenious defects can selectively accelerate the adsorption of OH⁻, thus enhancing the electrochemical activity. The D-NiFeAl-LDHs electrocatalyst had higher OER electrocatalytic activity than NiFe-LDHs electrocatalyst: its accelerated OER kinetics were mainly due to the introduction of iron and nickel defects in NiFeAl-LDHs nanosheets, which effectively adjusted the surface electronic structure and improved OER electrocatalytic performance. There was only a low overpotential of 262 mV with the current density of 10 mA cm⁻², and the Tafel slope was as low as 41.67 mV dec⁻¹. The OER electrocatalytic performance of D-NiFeAl-LDHs was even better than those of most of the reported NiFe-LDHs electrocatalysts.     

Surfactant-assisted hydrothermal synthesis of nitrogen doped Mo2C@C composites as highly efficient electrocatalysts for hydrogen evolution reaction

We describe a facile surfactant-assisted hydrothermal route to synthesize nitrogen doped Mo₂C@C composites in the presence of cetyltrimethylammonium bromide (CTAB) as carbon source and structure guiding agent. The resulting Mo₂C@C composites consist of Mo₂C nanocrystals with sheet-like morphology and well-dispersed nitrogen element doping. Controllable experiments indicate that the additive amount of CTAB can efficiently tune porous structure and electrochemical activity of the as-prepared Mo₂C@C materials. This unique nitrogen doped Mo₂C@C composite provides several advantages for electrocatalytic applications: (1) nitrogen doped carbons can prevent the aggregation of Mo₂C nanocrystals and render it high conductivity; (2) the homogeneous dispersion of Mo₂C nanocrystals provides abundant active sites; (3) 2D morphology, the hierarchical porosity, and high surface areas allow large exposed field of active sites and facilitate mass transfer. As a result, the nitrogen doped Mo₂C@C composites deliver superior HER electrocatalytic activities with a low overpotential of only 100 mV and also a low Tafel slope of 53 mV/dec in alkaline condition. Such CTAB-assisted strategy may open up an opportunity towards synthesis of low cost and high performance Mo-based electrocatalysts for various applications, such as water splitting.     

FeNi3/Ni2P heterojunction encapsulated in N-doped carbon nanotubes as an effective electrocatalyst for oxygen evolution reaction

Heterojunction construction is a vital strategy for the preparation of oxygen evolution reaction (OER) electrocatalysts by adjusting electronic properties. Herein, the heterojunction electrocatalyst consisting of FeNi₃/Ni₂P nanoparticles encapsulated in N-doped carbon nanotubes (FeNi₃/Ni₂P@NCNTs) was obtained by a simple synthetic method. FeNi₃/Ni₂P@NCNTs heterojunction effectively promoted the interface charge transfer between different components. Moreover, the prepared catalyst FeNi₃/Ni₂P@NCNTs exhibited extraordinary catalytic activity for OER in alkaline medium. The η₁₀, Tafel slope, C_dl for OER were 298 mV, 81.82 mV dec⁻¹ and 14.35 mF cm⁻², respectively. Besides, no visible variation after stability test for 100 h continuously. Remarkable catalytic activity is given the credit to the autocatalytic growth of carbon nanotubes, the synergistic effect of Ni₂P and FeNi₃ on the interface of heterojunction and the optimized electronic structure.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

Hexagonal CoFe2O4/β-Ni(OH)2 heterojunction composite as an advanced electrocatalyst for the oxygen evolution reaction

Transition metal-based heterostructure materials are considered as promising alternatives to state-of-the-art noble metal-based catalysts toward the oxygen evolution reaction (OER). Herein, for the first time, a simple interface engineering strategy is presented to synthesize efficient electrocatalysts based on a novel CoFe₂O₄/β-Ni(OH)₂ heterogeneous structure for the electrochemical OER. Remarkably, the optimized CoFe₂O₄/β-Ni(OH)₂ electrocatalyst, benefiting from its hierarchical hexagonal heterostructure with strong electronic interaction, enhanced intrinsic activity, and electrochemically active sites, exhibits outstanding OER electrocatalytic performance with a low overpotential of 278 mV to reach a current density of 10 mA cm⁻², a small Tafel slope of 67 mV dec⁻¹, and long-standing durability for 30 h. Its exceptional OER performance makes the CoFe₂O₄/β-Ni(OH)₂ heterostructure a prospective candidate for water oxidation in alkaline solution. The proposed interface engineering provides new insights into the fabrication of high-performance electrocatalysts for energy-related applications.     

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo₂C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo₂C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo₂C (Mo₂C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo₂C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec⁻¹) and overpotential of 186.6 mV to drive current density of 10 mAcm⁻². It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.     

Structure and electrocatalytic hydrogen evolution performance of Mo2C thin films prepared by magnetron sputtering

Mo₂C, which has a unique electronic structure similar to the electronic structure of Pt, is considered as the material with the greatest potential to replace Pt as a catalyst for the electrocatalytic hydrogen evolution reaction (HER). However, Mo₂C thin films have not attracted enough attention in the field of electrocatalysis. This work proposes a method for preparing Mo₂C thin films as a catalyst for electrocatalytic HER through radiofrequency magnetron sputtering. The HER activity of the Mo₂C thin film in acidic and alkaline media is studied by changing the deposition power of the Mo₂C target and doping Ni for structural modification. Results show that increasing the deposition power of Mo₂C can significantly enhance the HER activity of the films in acidic and alkaline media, and metal Ni doping can further enhance the HER activity of the Mo₂C films. In an alkaline environment at a current density of 10 mA cm⁻², the films demonstrate an overpotential of as low as 163 mV with a Tafel slope of 107 mV·dec⁻¹. In acidic media, the films present the corresponding overpotential of 201 mV and a Tafel slope of as low as 96 mV·dec⁻¹. Moreover, the Ni-doped Mo₂C films have excellent HER stability. The synergy between doped Ni and Mo vacancies optimizes the strength of the Mo–H bond and the adsorption and desorption equilibrium of active H, thus enhancing HER kinetics. This work guides the possible structural design of Mo₂C thin films for electrocatalytic HER.     

Local electronic structure modulation of NiVP@NiFeV-LDH electrode for high-efficiency oxygen evolution reaction

The emergence of alternative sustainable energy technologies has stimulated the utilisation of high-efficiency, cost-effective electrodes for renewable energy conversion. The oxygen evolution reaction (OER) is critical for water splitting and rechargeable metal-air batteries. However, the identification of efficient and robust non-noble-metal-based OER electrocatalysts remains a major hurdle for large-scale hydrogen production. Herein, NiVP@NiFeV-LDH heterojunction catalysts were constructed by phosphidation and hydrothermal processing, because OER activity can be improved by coupling NiVP and NiFeV-LDH. NiVP@NiFeV-LDH/NF exhibited remarkable OER performance with an ultralow overpotential of 317 mV at a current density of 100 mA cm⁻² and a Tafel slope of 83.0 mV dec⁻¹ in an alkaline environment. The high efficiency of NiVP@NiFeV-LDH/NF is attributed to increased mass and electron transport because of array structure formation and interfacial electronic structure optimisation, respectively. This work provides a novel approach for augmenting the OER performance of non-noble-metal-based electrocatalysts for energy conversion applications.     

Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH)₂/NiCo₂O₄ heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH)₂/NiCo₂O₄ (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm⁻² for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm⁻². The improved catalytic performance of the Ni(OH)₂/NiCo₂O₄ heterojunctions is attributed to the chemical synergic combining of Ni(OH)₂ and NiCo₂O₄, large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.     

Engineering bimetallic cactus-like NiFeOOH/CoNiSe2 heterostructure nanosheets for efficient oxygen evolution and overall water splitting

The development of structural stable, high-performance, inexpensive electrocatalysts for oxygen evolution reactions (OER) is essential to alleviate the energy crisis. Herein, cactus-like CoNiSe₂ was synthesized on nickel foam and NiFeOOH was electrodeposited on surface of CoNiSe₂ to form a core-shell structural electrode. The obtained NiFeOOH/CoNiSe₂/NF exhibited ultra-low overpotentials of 204 mV and 234 mV at 10 and 100 mA cm⁻², with a Tafel slope of 26.2 mV dec⁻¹ in 1 M KOH alkaline solution. Furthermore, the current density only decreased by 5% after a 100 h durability test at 200 mA cm⁻², showing excellent robust stability. A two-electrode system with NiFeOOH/CoNiSe₂/NF as anode and Ni/NiO@MoO_3-x/NF as cathode (NiFeOOH/CoNiSe₂/NF||Ni/NiO@MoO_3-x/NF) showed a low voltage of 1.47/1.56 V to deliver 10/100 mA cm⁻². According to the experimental and density functional theory (DFT) results, the strong electronic interactions at the NiFeOOH/CoNiSe₂/NF interface leads to an increase in the valence state of Fe and an optimisation of the adsorption free energy, which are favourable to reduce the energy consumption of the OER. This work obtained high performance OER electrocatalysts by engineering amorphous and crystalline heterointerfaces and structural design, which will provide some inspiration for similar work.     

Ultrathin MoS2 nanosheets in situ grown on rich defective Ni0.96S as heterojunction bifunctional electrocatalysts for alkaline water electrolysis

Developing earth-abundant and highly active bifunctional electrocatalysts are critical to advance sustainable hydrogen production via alkaline water electrolysis but still challenging. Herein, heterojunction hybrid of ultrathin molybdenum disulfide (MoS₂) nanosheets and non-stoichiometric nickel sulfide (Ni_0.96S) is in situ prepared via a facile one-step hydrothermal strategy, followed by annealing at 400 °C for 1 h. Microstructural analysis shows that the hybrid is composed of intimate heterojunction interfaces between Ni_0.96S and MoS₂ with exposed active edges provided by ultrathin MoS₂ nanosheets and rich defects provided by non-stoichiometric Ni_0.96S nanocrystals. As expected, it is evaluated as bifunctional electrocatalysts to produce both hydrogen and oxygen via water electrolysis with a hydrogen evolution reaction (HER) overpotential of 104 mV at 10 mA cm⁻² and an oxygen evolution reaction (OER) overpotential of 266 mV at 20 mA cm⁻² under alkaline conditions, outperforming most current noble-metal-free electrocatalysts. This work provides a simple strategy toward the rational design of novel heterojunction electrocatalysts which would be a promising candidate for electrochemical overall water splitting.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

Ir-doped Co3O4 as efficient electrocatalyst for acidic oxygen evolution reaction

Oxygen evolution reaction (OER) is an important bottleneck for large-scale acidic water splitting applications due to its sluggish reaction kinetics. Therefore, the development of highly active, stable, and inexpensive electrocatalysts for OER remains a challenge. Herein, we develop the iridium doped Co₃O₄ (Ir–Co₃O₄) with low Ir content of 2.88 wt% for efficient acidic OER. Considering systemic characterizations, it is probably concluded that Ir can be uniformly doped into the lattice of Co₃O₄ and induce a certain distortion. The electrochemical results reveal that Ir–Co₃O₄ nanoparticles demonstrate significantly enhanced electrocatalytic OER activity and stability in 0.5 M H₂SO₄ solution compared with pure Co₃O₄, in which the overpotential at the current density of 10 mA cm⁻² decreases from 382 mV to 225 mV and the value of Tafel slope decreases from 101.7 mV dec⁻¹ to 64.1 mV dec⁻¹. Besides, Ir–Co₃O₄ exhibits excellent electrocatalytic durability for continuous 130 h's test without any activity attenuation. Moreover, this work provides a kind of high-performance acidic OER electrocatalyst for the development of hydrogen energy.     

Prepation of perovskite oxides/(CoFe)P2 heterointerfaces to improve oxygen evolution activity of La0.8Sr1.2Co0.2Fe0.8O4+δ layered perovskite oxide

Constructing heterointerfaces with optimized electronic structures is an alternative strategy to improve the electrocatalytic activity for oxygen evolution reaction (OER). As a proof-of-concept, in this communication, we tailor the unique perovskite oxides/(CoFe)P₂ heterointerfaces on the surface of La_0.8Sr_1.2Co_0.2Fe_0.8O_4+δ (LSCF) layered perovskite oxides through an in-situ reducing and phosphating process. XRD, SEM and TEM characterizations show that island-like (CoFe)P₂ nanoparticles with a diameter of ~20 nm are generated, which adjusts the oxygen vacancy of perovskite oxides and accelerates the charge transfer during the OER. As a result, a small OER overpotential of 350 mV at 10 mA cm⁻², an excellent OER activity with a Tafel slope of 64 mV dec⁻¹ and a stability over 1000 cycles are obtained, which outperform commercial IrO₂ and most reported perovskite oxides based electrocatalysts.     

Green synthesis of CuCo2O4–CuO composite nanoparticles grown on nickel foam for high-performance oxygen evolution reaction

Among the most critical components for water-derived hydrogen fuel, the study of electrocatalysts as anode for the oxygen evolution reaction (OER) is an important topic in the water splitting process. In this work, the CuCo₂O₄–CuO composite electrode is synthesized directly on nickel foam to evaluate its potential as OER catalyst in an alkaline medium. An interesting strategy is to use flaxseed oil as a polymerizing agent in a sol-gel process combined with hydrothermal. A low overpotential value of 289 mV vs RHE at 10 mA cm⁻² current density and a Tafel slope of 71 mV dec⁻¹ were observed, which represents an electrocatalytic performance superior to other Cu and Co based oxides in the literature. Short-term stability testing of 15 h demonstrates stable overpotential with no observable secondary phase after measurements. The successful outcome of this work is a result of the promising green chemical approach herein used to obtain electrocatalysts grown directly on conductive substrates for water oxidation.     

Iron-substituted Co-Ni phosphides immobilized on Ni foam as efficient self-supported 3D hierarchical electrocatalysts for oxygen evolution reaction

Electrocatalytic water splitting for hydrogen evolution is significantly impeded by the kinetically sluggish oxygen evolution reaction (OER). Thus, the development of highly efficient and durably stable non-noble-metal OER electrocatalyst is necessary and challenging for the large-scale electrocatalytic water splitting. Herein, a series of iron-substituted cobalt-nickel phosphides grown on Ni foam (FeCoNi-P/NFs) were easily prepared though successive hydrothermal and phosphorization treatments. The chemical compositions, crystalline and electronic structures as well as surface morphologies of these resulting electrocatalysts are strongly related with the iron substitution ratio. More interestingly, the FeCoNi-P/NF-2 nanosheet arrays prepared from equivalent molar ratio of iron and cobalt precursors exhibit the best OER performance with a low overpotential of 266 mV to produce a current density of 50 mA cm⁻² and a low Tafel slope of 61.2 mV dec⁻¹ in 1.0 M KOH condition, which is comparable to the reported state-of-the-art OER electrocatalysts. Additionally, the FeCoNi-P/NF-2 nanosheet arrays also show satisfactory long-term durability over 60 h. The superior OER activity of the electrocatalyst is essentially attributed to the heteroatomic substitution and the unique three-dimensional hierarchical morphology, which greatly increase the electrical conductivity, afford more active sites and facilitate the efficient charge transfer ability.     

Spinel NiCo2O4 3-D nanoflowers supported on graphene nanosheets as efficient electrocatalyst for oxygen evolution reaction

Efficient oxygen evolution reaction (OER) electrocatalysts with non-noble metals are very critical for the large-scale exploitation of electrocatalytic hydrogen production systems. To improve the catalytic activity of OER electrocatalysts, several design strategies, such as construction of nanostructures, porous structures and composite materials have been proposed. Herein, spinel NiCo₂O₄ 3-D nanoflowers supported on graphene nanosheets (GNs) are prepared by a simple solvothermal synthesis method as non-noble metal electrocatalysts for OER. The present NiCo₂O₄/GNs composite integrates multiple advantages of nanostructures, porous structures and composite materials, including high surface area, abundant catalytic sites and high stability. Benefiting from the favorable features, the NiCo₂O₄/GNs composite exhibits a better OER performance than NiCo₂O₄ and RuO₂ in alkaline medium, which has a low onset potential (1.50 V), a small Tafel slope (137 mV dec⁻¹). The present work opens a new window for the construction of the carbon-supported 3-D nanostructure of transition metal catalysts with optimizable electrocatalytic performances for electrocatalytic hydrogen production.     

Tailoring Cr doped NiFeP nanoparticles embedded in 3D cellulose nanofibrils carbon architecture for efficient oxygen evolution reaction

Oxygen evolution reaction (OER) is considered the bottleneck that restricting the pace of electrocatalytic hydrogen production. Modulating structure and heterogeneous doping are essential approaches to effectively promote the electrocatalytic efficiency and stability. Herein, three-dimensional (3D) porous Cr doped NiFeP nanoparticles encapsulated in cellulose nanofibrils (CNF) carbon architecture (Cr–NiFeP/NC) with high-efficiency and durable OER performance was constructed. CNF played crucial role on the construction of 3D porous framework and promoting the OER performance significantly. Benefiting from the 3D porous structure, high specific surface area and exposed abundant active sites, the Cr–NiFeP/NC electrocatalyst displayed excellent OER performance, which the overpotential to deliver the current density of 10 mA cm⁻² was only 249 mV with a Tafel slope of 51.2 mV dec⁻¹ in 1.0 M KOH, outperforming the RuO₂ and other reported electrocatalysts remarkably. In addition, the Cr–NiFeP/NC electrocatalyst exhibited outstanding stability, which the overpotential was only increased by 2.5% after 48 h chronopotential measurement to deliver a current density of 10 mA cm⁻² with stable morphology and structure. This work demonstrated an integrated strategy of Cr doping and 3D porous structure modulating employed CNF as skeleton for the efficient and durable OER performance, providing a spark for hydrogen production by water splitting.