Benchmark Current Density Research Articles

In-situ assemblage of Fe–V–P/graphene aerogel based on prussian blue analogue as a high-performance electrocatalyst for oxygen evolution reaction

The carbon scaffold with high conductivity is suitable to enhance the catalytic activity of prussian blue analogues (PBAs) in oxygen evolution reaction (OER) of water splitting. Herein, a two-step strategy is developed to synthesize Fe–V–P/graphene aerogel based on prussian blue analogue (Fe–V–P/GA) electrocatalysts, which possess dense arrangement of anomalous octahedron structure. In the vanadium-modified PBAs (FeV–PBAs), Fe/V with a series of different molar ratios has been investigated and when the molar ratio of Fe/V is 1:1, the catalyst achieves a fairly high specific surface area expressed by the double-layer capacitance of 5.29 mF cm−2 and requires overpotentials of only 234.0 and 314.3 mV to attain the benchmark current density of 10 and 50 mA cm−2 during OER process. Besides, the catalyst owns satisfactory stability and the current density remains almost constant during stability tests lasting up to 70 h. As revealed via electrochemical kinetics analysis and the spectroscopic measurement, embellished FeV–PBAs not only lead to larger tangible area, more accessible sites and higher durable stability, but also provide formation of high valence state of iron and vanadium species, strong modification of electronic state and faster kinetics. This study provides a novel mode of thinking to consummate the design of 3D construction so as to boost the catalytic effect of transition metal catalysts for efficient oxygen evolution.

Metal-organic frameworks derived interfacing Fe2O3/ZnCo2O4 multimetal oxides as a bifunctional electrocatalyst for overall water splitting

Exploring highly effective, long-lasting, and earth-abundant catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is very important to improve the next-generation water-splitting process. Herein, we report the Fe2O3/ZnCo2O4 heterointerface nanocomposite derived from trimetallic metal-organic frameworks (MOFs), which has been considered a promising electrode catalyst material for overall water splitting, including bifunctional HER and OER performances. However, there is no study being reported yet on the Fe2O3/ZnCo2O4 polyhedron morphology for HER, OER, and overall water-splitting activities. The synergic effect or heterointerface engineering between the Fe2O3 and ZnCo2O4 is advantageous for improved active sites, effective charge transfer, and the long-term stability of the composite. This electrocatalyst shows enhanced HER and OER performances in terms of low overpotential of 44.8 mV and 212 mV to achieve a benchmark current density of 10 mAcm−2. Moreover, the two-electrode water electrolyzer can achieve a current density of 10 mAcm−2 at a small cell voltage of 1.44 V. Our findings in this study can motivate further research to focus on the MOFs-derived trimetallic metal oxide electrocatalysts for next-generation water-splitting devices.

Prussian blue-derived hollow carbon-wrapped Fe-doped CoS2 nanocages as durable electrocatalyst for efficient hydrogen evolution

Cobalt disulfide (CoS2) is regarded as a low cost and abundant non-noble electrocatalyst, but some drawbacks limit its application due to its sluggish intrinsic electrocatalytic kinetics and high hydrogen evolution overpotential. In this work, carbon-wrapped Fe-doped CoS2 nanocages (C/Fe–CoS2) were synthesized via gradual sulfurization of cobalt hexacyanoferrate and evaluated as electrocatalysts for hydrogen evolution reaction (HER). The nanocage architecture exposes more electrochemically active site, and carbon wrapping reduces the agglomeration of C/Fe–CoS2 and optimizes the electronic structure, while the Fe doping decreases the hydrogen adsorption free energy of CoS2. Therefore, C/Fe–CoS2 demonstrates a superior HER performance, showing a benchmark current density of 10 mA cm−2 at the low overpotential of 151 mV in acidic electrolyte and a remarkable stability (cyclic voltammetry cycling for 3000 cycles and continuous electrolysis at the overpotential of 180 mV for 25,000 s). The as-designed C/Fe–CoS2 should be one of the most promising catalysts for HER application. This strategy highlights the construction of high performance electrocatalysts via structure designing and heteroatom doping for efficient and stable hydrogen generation.

Elucidating Catalytic Sites Governing the Performance toward the Hydrogen Evolution Reaction in Ternary Nitride Electrocatalysts

Proton exchange membrane electrolyzers are considered the most advanced devices for producing green hydrogen by water electrolysis. Their development requires catalytic materials that are stable under acidic conditions and drive the hydrogen evolution reaction (HER) forward efficiently which makes research into the identification of the catalytic sites important. We report that free-standing Co2Mo3N and Ni2Mo3N achieve overpotentials of 149 ± 8 and 158 ± 10 mV (in 0.5 M H2SO4) at a benchmark current density of 10 mA cm–2. Both nitrides remained stable and consistently deliver current densities >500 mA cm–2 at a potential as low as 308 ± 22 mV when they were immobilized on nickel foam. Replacing Ni for Fe in Ni2Mo3N leads to FexNi2–xMo3N (0.5 ≤ x ≤ 1.25) that show a decrease in catalytic activity as the value of x increases which confirms that Ni (rather than Mo and N) sites are catalytically active. The X-ray photoelectron spectroscopy data additionally suggests that preserving the low oxidation states of transition metals in the nitrides is important for achieving good catalytic performance toward the HER in acidic electrolytes.

Evolution of Carbonate-Intercalated γ-NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation.

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon-neutral economy. In this aspect, the low-temperature, single-source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [NiII (PyHS)4 ][OTf]2 (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255mV to reach the benchmark current density of 10mAcm-2 and shows 63h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate-intercalated γ-NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine-based organic substrates to value-added chemicals, with high efficiencies.

Combustion-derived BaNiO3 nanoparticles as a potential bifunctional electrocatalyst for overall water splitting

Electrochemical water electrolyser though an assuring solution for clean hydrogen production, the sluggish kinetics and high cost of existing precious metal electrocatalyst remains a barrier to its effective utilization. Herein, solution combustion route derived perovskite type barium nickelate (BaNiO3) nanoparticles were developed and studied for their bifunctional electrocatalytic properties towards overall water splitting. The unannealed BaNiO3 nanoparticles exhibited the highest OER and HER activity with overpotentials 253 mV and 427 mV respectively to attain 10 mAcm−2 in 1.0 M KOH. Using unannealed BaNiO3 as a bifunctional electrocatalyst in a two-electrode alkaline electrolyser, the cell was able to achieve the benchmark current density at a low cell voltage of 1.82 V. Impressively the setup's electrocatalytic performance improved 4.9% after continuous overall water splitting for 24 h at 30 mAcm−2. Therefore, BaNiO3 nanoparticles can be a low-cost and efficient alternative for noble metal electrocatalysts for clean H2 production.

Entropy-Stabilized Multicomponent Porous Spinel Nanowires of NiFeXO4 (X = Fe, Ni, Al, Mo, Co, Cr) for Efficient and Durable Electrocatalytic Oxygen Evolution Reaction in Alkaline Medium.

Cost-effective electrochemical water splitting technology hinges on the development of efficient and durable catalysts for oxygen evolution reaction (OER). Spinel oxides (formula: AxB3-xO4) are structurally stable for real applications. Much effort has been devoted to improving the catalytic activity. Here, we report a eutectic dealloying strategy to activate the porous spinel NiFe2O4 nanowires with up to four metal cation substitutions. As-obtained spinel NiFeXO4 (X = Fe, Ni, Al, Mo, Co, Cr) delivers a benchmark current density of 10 mA·cm-2 at an overpotential of only 195 mV, outperforming most spinel phase OER electrocatalysts and comparable to the state-of-the-art NiFe hydroxides. It is stable for over 115 h of electrolysis. Aberration-corrected transmission electron microscopy, high-resolution electron energy loss spectroscopy, and atomic-scale strain mappings reveal that the multivalent cation substitutions result in substantial lattice distortion and significant electronic coupling of metal 3d and O 2p orbitals for increased covalency. Further theoretical calculations suggest that the NiFeXO4 are stabilized by the high configurational entropy, and their synergy favors the absorption of H2O molecules and lowers the adsorption energy barrier of the OOH* intermediate. The improved intrinsic activity together with the highly nanoporous structures contribute to the appealing apparent catalytic performances. The work demonstrates an effective approach for the synthesis of stable multicomponent spinel oxides and highlights the effectiveness of the multication substitution strategy for producing highly durable and active spinel catalysts, which meet multiplexed structure and superior property requirements in practical applications.

Electrochemical Performance Evaluation of Bimetallic Sulfide Nanocomposite with Fullerene (CeNdS/C60) for Efficient Oxygen Evolution Reaction (OER)

In recent decades, developing cost-stable electrocatalysts for oxygen evolution reactions at low overpotential has still been challenging for chemical energy conversion devices. In the present work, we have reported the facile development of the CeNdS/C60 nanocomposite via the solution method. The covered C60 over CeNdS is confirmed by TEM and STEM, providing strong interfacial interaction between CeNdS and C60. In a medium consisting of 1.00 M KOH, CeNdS/C60 electrode displayed a very small overpotential of 346 mV and a small Tafel slope of 68 mV dec–1 at a benchmark current density. Chronoamperometric and continuous CV sweeps confirmed the good stability of this catalyst at a scan rate of 5 mV s–1 (5000 cycles). The turnover frequency of CeNdS/C60 was 1.7 s–1, and the corresponding electrochemically active surface area was 3057.5 cm2. Brunauer–Emmett–Teller (BET) surface area results also confirmed the attachment of C60 particles with CeNdS by developing a high surface area with porous channels that further facilitate electrolyte penetration and the charge transfer rate, thus improving the OER property of CeNdS/C60. All performed techniques showed that the presence of Nd and C60 ions in the CeNdS/C60 catalyst is responsible for growing the superb intrinsic OER catalytic activity. Furthermore, these findings have revealed an excellent potential for CeS-based electrocatalysts for more electrochemical energy-conversion applications.

F and rare V4+ doped cobalt hydroxide hybrid nanostructures: excellent OER activity with ultralow overpotential.

Highly efficient and stable Earth abundant transition metal electrocatalysts are in great demand for the oxygen evolution reaction (OER), a bottleneck process involved in the water splitting reaction and metal-air batteries. Herein, we have demonstrated a single step direct fabrication of cobalt hydroxide (Co(OH)2) nanowires doped with vanadium(V) in a less stable +4 oxidation state and fluoride (F) ions (V-Co(OH)2) on a carbon cloth electrode that showed highly enhanced OER activity under alkaline conditions. V-Co(OH)2 nanowires synthesized under the optimized conditions produced excellent OER activity with an ultralow overpotential of 136 mV at 10 mA cm-2 (scan rate 1 mV s-1), a small Tafel slope (51.6 mV dec-1) and good stability over 72 h. To the best of our knowledge, this is the lowest overpotential reported for cobalt-based electrocatalysts to achieve a geometric current density of 10 mA cm-2. The controlled synthesis and HR-TEM studies revealed the formation of hybrid nanostructures (nanowires along with spherical assembly of nanoparticles) and codoping of V and F ions played an important role in enhancing the OER activity. The detailed chemical composition and oxidation state analysis by X-ray photoelectron spectroscopy (XPS) confirmed the doping of V4+ and ionic F in V-Co(OH)2 with mixed valence states of Co2+/Co3+ and a higher Co2+ ratio. The outstanding OER activity of V-Co(OH)2 is attributed to the formation of a spherical assembly of nanoparticles with nanowires, which provided a high number of catalytically active sites with enhanced charge transport, and doping of higher valence V4+ and strongly electronegative F in V-Co(OH)2 with a higher ratio of Co2+/Co3+ promoted OOH* intermediate generation and significantly boosted the OER activity. Overall, the present work highlights the possibility of achieving highly active Earth abundant OER electrocatalysts by controlling the mixed oxidation state of Co with a judicious choice of dopants along with maintaining optimal nanostructure morphologies.

Structure and magnetic properties of an amine-templated one-dimensional cobalt-fluoro-sulfate containing Co4F4 cubane and hydrogen evolution reaction (HER) performance of its derived carbon-wrapped CoSe2 nanorods.

Amine-templated 1D cobalt fluoro sulfate of the composition [(CH3)2NH2]2[Co4F4(SO4)3(C3N2H4)4], consisting of Co4F4 cubane-type secondary building unit, has been synthesized under solvothermal condition. The magnetic properties of the Co4F4 cubane chain exhibited a low-temperature magnetic ordering below 17 K (Tc) attributed to intra-cluster ferromagnetic coupling and did not show spin-glass freezing. The selenylation of the Co4F4 cubane chain leads to the formation of sphere-like CoSe2 in the hydrothermal route (CoSe2@HT). At the same time, nanorods of CoSe2 encapsulated with carbon matrix were obtained in a sealed tube method (CoSe2@ST). Moreover, CoSe2@ST exhibited a higher hydrogen evolution reaction (HER) activity than CoSe2@HT in an acidic medium with 177 mV overpotential to achieve the benchmark current density of 10 mA cm-2. The promising HER performance of derived CoSe2@ST could be attributed to an increase in the geometrical and specific activity due to the encapsulation of N-doped carbon matrix over the CoSe2 nanorods that facilitate faster charge transfer at the electrode-electrolyte interface and higher electrochemical conductivity than the derived CoSe2@HT. This work demonstrates a low-temperature, solvent- and reducing agent-free new synthetic approach for synthesizing framework-derived materials.

1-D arrays of porous Mn0.21Co2.79O4 nanoneedles with an enhanced electrocatalytic activity toward the oxygen evolution reaction.

Developing effective electrocatalysts for the oxygen evolution reaction (OER) that are highly efficient, abundantly available, inexpensive, and environmentally friendly is critical to improving the overall efficiency of water splitting and the large-scale development of water splitting technologies. We, herein, introduce a facile synthetic strategy for depositing the self-supported arrays of 1D-porous nanoneedles of a manganese cobalt oxide (Mn0.21Co2.79O4: MCO) thin film demonstrating an enhanced electrocatalytic activity for OER in an alkaline electrolyte. For this, an MCO film was synthesized via thermal treatment of a hydroxycarbonate film obtained from a hydrothermal route. The deposited films were characterized through scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In contrast to a similar 1D-array of a pristine Co3O4 (CO) nanoneedle film, the MCO film exhibits a remarkably enhanced electrocatalytic performance in the OER with an 85 mV lower overpotential for the benchmark current density of 10 mA cm-2. In addition, the MCO film also demonstrates long-term electrochemical stability for the OER in 1.0 M KOH aqueous electrolyte.

Highly enhanced electrocatalytic OER activity of water-coordinated copper complexes: effect of lattice water and bridging ligand.

The use of metal-organic compounds as electrocatalysts for water splitting reactions has gained increased attention; however, a fundamental understanding of the structural requirement for effective catalytic activity is still limited. Herein, we synthesized water-coordinated mono and bimetallic copper complexes (CuPz-H2O·H2O, CuPz-H2O, CuBipy-H2O·H2O, and CuMorph-H2O) with varied intermetallic spacing (pyrazine/4,4'-bipyridine) and explored the structure-dependent oxygen evolution reaction (OER) activity in alkaline medium. Single crystal structural studies revealed water-coordinated monometallic complexes (CuMorph-H2O) and bimetallic complexes (CuPz-H2O·H2O, CuPz-H2O, CuBipy-H2O·H2O). Further, CuPz-H2O·H2O and CuBipy-H2O·H2O contained lattice water along with coordinated water. Interestingly, the bimetallic copper complex with lattice water and shorter interspacing between the metal centres (CuPz-H2O·H2O) showed strong OER activity and required an overpotential of 228 mV to produce a benchmark current density of 10 mA cm-2. Bimetallic copper complex (CuPz-H2O) without lattice water but the same intermetallic spacing and bimetallic complex with increased interspacing but with lattice water (CuBipy-H2O·H2O) exhibited relatively lower OER activity. CuPz-H2O and CuBipy-H2O·H2O required an overpotential of 236 and 256 mA cm-2, respectively. Monometallic CuMorph-H2O showed the lowest OER activity (overpotential 271 mV) compared to bimetallic complexes. The low Tafel slope and charge transfer resistance of CuPz-H2O·H2O facilitated faster charge transfer kinetics at the electrode surface and supported the enhanced OER activity. The chronoamperometric studies indicated good stability of the catalyst. Overall, the present structure-electrocatalytic activity studies of copper complexes might provide structural insight for designing new efficient electrocatalysts based on metal coordination compounds.

Pt-Doped Biomass Carbon Decorated with MoS2 Nanosheets as an Electrocatalyst for Hydrogen Evolution

It is necessary to develop an efficient hydrogen evolution catalyst to improve the efficiency of the hydrogen evolution reaction (HER). Herein, a MoS2 nanosheet is decorated on the Pt-doping biomass yeast cells (MoS2@Pt/YC) via a simple hydrothermal process. Reducing the noble metal loading without compromising its performance is a challenging task. The smooth surface of YCs is conducive to the growth of MoS2 nanosheets, and its functional groups provide attachment sites for metal Pt. The Pt/YC is covered with MoS2 nanosheets, thus improving the exposed active sites for HER. The obtained MoS2@Pt/YC delivers a competitive overpotential of 118 mV at the benchmark current density of 10 mA cm-2 and achieves a small Tafel slope of 74 mV dec-1, indicating the great HER performance of MoS2@Pt/YC. Moreover, MoS2@Pt/YC shows robust stability after 24 h of continuous operation toward HER in acidic solution. By introducing transition metal sulfides with high specific surface area, the loading of precious metals can be reduced without compromising properties. This work provides a method to design Pt-doping HER electrocatalysts through a simple method. The facile preparation process for MoS2@Pt/YC and its outstanding performance allow it to be a promising electrocatalyst for practical HER application.

Tuning of electrocatalytic activity of mixed metal dichalcogenides supported NiMoP coatings for alkaline hydrogen evolution reaction

The mixed metal dichalcogenides combination of WS2–MoS2 was coated onto Cu substrate by electroless NiMoP plating technique and the electrocatalytic hydrogen evolution reaction (HER) performance was investigated. The enhanced structural, morphological parameters and boosted electrocatalytic performance of the various metal-metal molar ratio of WS2–MoS2 onto NiMoP plate were identified under variable operating conditions and it was successfully evaluated by various characterization techniques. The well-defined crystalline nature, phase, particle size, structure, elemental analysis and surface morphology of prepared coatings were analyzed by FESEM, XRD, AFM and EDS mapping. The electrochemical analysis was performed using open circuit potential (OCP) analysis, chronoamperometry (CA), electrochemical impedance spectroscopy (EIS), Tafel curves, linear sweep voltammetry (LSV), cyclic voltammetry (CV) and polarization studies to find the activity of prepared electrocatalyst towards electrochemical hydrogen evolution reactions. The performance of bare NiMoP and WS2–MoS2/NiMoP plates were compared and found that the HER activity of NiMoP can be reinforced by composite incorporation through the synergic effect arises with in the catalytic system, which improves surface roughness and enhances the magnitude of electrocatalyst toward HER. The achievement of enhanced catalytic performance of coatings was authenticate by the kinetic parameters such as decreases in Tafel slope (98 mV dec−1), enhanced exchange current densities (9.32 × 10−4 A cm−2), and a lower overpotential. The consistent performance and durability of the catalyst were also investigated. The enhanced electrocatalytic activity of WS2–MoS2/NiMoP coatings increased with respect to the surface-active sites associated with combination of mixed dichalcogenides and the synergic effect arises in between different components present in the coating system. This work envisages the progressive strategies for the economical exploration of a novel WS2–MoS2/NiMoP water splitting catalyst used for large scale H2 generation. The prepared WS2–MoS2/NiMoP embedded Cu substrate possess high catalytic activity due to its least overpotential of 101 mV at a benchmark current density of 10 mA cm−2, which demonstrated the sustainable, efficient and promising electrocatalytic property of prepared catalyst towards HER under alkaline conditions.

Stabilization of Ru NPs over 3D LaCrO3 Nanostructures for High-Performance HER Catalysts in Acidic Media.

Hydrogen is considered as one of the best alternatives to carbon-based fossil fuels as energy sources. Electrocatalytic water splitting is one of the finest and eco-friendly methods for the production of hydrogen as compared to all other methods such as stream reforming carbon, hydrolysis of metal hydrides, etc. However, the sluggish kinetics on both the half-cell reactions limits the large-scale production of hydrogen. Hence, to overcome such kind of kinetic issues, designing a catalyst with characteristics of low overpotential and high stability is a matter of prime importance for the research community. Perovskite oxides are one of the well-documented materials for their excellent electrocatalytic water oxidation activity. But because of the lack of a proper proton adsorption site, these materials are unable to show proper hydrogen evolution reaction (HER) activity. Several strategies have been adopted for improving the HER activity of perovskite materials like cation doping, nanostructuring, etc. Here in this work, we prepared a shape-selective LaCrO3 (LCO) material. To enhance the electrocatalytic activity, we decorated the LCO with Ru nanoparticles via a hydrothermal method with different concentrations of Ru (Ru@LaCrO3), coined LCOn (n = 1-2.5). The as-synthesized RLCO2.5 showed the highest HER activity by demanding a low overpotential of 150 mV, whereas bare LCO demanded a higher overpotential of 364 mV to reach the benchmark current density of 10 mA/cm2. Also, RLCO2.5 showed a very low Rct value of 15.8 Ω and followed the facile kinetics with a lower Tafel value of 101 mV/dec. It also showed excellent stability over 55 h at a current density of 10 mA/cm2 in chronoamperometry studies. Acceleration degradation studies of RLCO2.5 showed comparably good activity with a small hike in overpotential toward HER. Hence, RLCO-based materials are highly helpful to develop efficient electrocatalysts to produce hydrogen in a large scale.

Two-dimensional double transition metal carbides as superior bifunctional electrocatalysts for overall water splitting

The development of bifunctional catalysts that can outperform precious metal electrocatalysts for overall water splitting is a critical task for sustainable green hydrogen production. Owing to the rich surface chemistry, unique physiochemical properties, and good stability, MXenes are considered efficient catalysts for hydrogen production. However, it is still a challenge to harmonize both HER (Hydrogen evolution reaction) & OER (Oxygen evolution reaction) reactions in the same media. Herein, we have reported the synthesis of Mo2TiC2Tx and Mo2Ti2C3Tx double transition metal carbides as NMP (non-precious metal) based bifunctional catalysts for overall water splitting in alkaline media. The LSV (linear sweep voltammetry) was employed for investigating catalytic activity, revealing the outstanding performance of Mo2TiC2Tx and Mo2Ti2C3Tx for high HER activity with an overpotential of 34 mV and 51 mV respectively, to reach a benchmark current density of 10 mAcm−2. The Mo2TiC2Tx also exhibited excellent OER activity with an overpotential of 320 mV as compared to 470 mV for Mo2Ti2C3Tx. The overall water splitting test uncovers a cell voltage of 1.57 V for Mo2TiC2Tx \\\\ Mo2TiC2Tx configuration. This study provides a comparison of two double transition MXene systems for effective use as bifunctional catalysts that opens new horizons for their use in clean hydrogen production.

Amorphous chromium oxide confined Ni/NiO nanoparticles-assembled nanosheets for highly efficient and stable overall urea splitting

Applications of urea oxidation reaction (UOR) in various sustainable energy-conversion systems are greatly hindered by its slow kinetics. Herein, we demonstrate an in-situ confined synthesis method that produces amorphous chromium oxide confined Ni/NiO nanoparticles-assembled nanosheets (Ni/NiO@CrOx) with fast reaction kinetics towards UOR. The confinement effect of the in-situ generated CrOx overlay contributes to ultrafine Ni/NiO nanoparticles, bringing about rich Ni/NiO and NiO/CrOx interfaces. In-situ Raman and electrochemical characterization show that both CrOx and metallic Ni can promote the formation of the NiOOH species and the electron transfer, leading to high intrinsic activity and fast reaction kinetics. At 1.40 V vs. reversible hydrogen electrode, the Ni/NiO@CrOx delivers a current density of 275 mA cm−2, which is about 2.6 and 6.1 times as large as those of the NiO@CrOx and NiO, respectively. In addition, the protective effect of the CrOx overlay leads to robust working stability towards UOR. Further, the Ni/NiO@CrOx nanosheets are used as bifunctional catalysts for overall urea splitting, and a small electrolysis cell voltage of 1.44 V is needed to reach the benchmark current density of 10 mA cm−2.

Constructing Ni-Modified Co-FcDA nanosheets for enhancing electrocatalytic oxygen evolution reaction

Electrocatalytic water splitting is an emerging technology for the development of maintainable hydrogen energy. It remains challenging to manufacture a stable, efficient, and cost-effective electrocatalyst that can conquer the slow reaction kinetics of water electrolysis. Herein, A metal-organic framework (MOF) based material is manufactured and productively catalyze the oxygen evolution reaction (OER). The introduction of elemental nickel enhances the catalytic activity of Co-FcDA. The results show that single Ni was well doped in the CoNi-FcDA catalysts and the doping of Ni has a great influence on the OER activity of CoNi-FcDA catalysts. CoNi-FcDA displayed a low overpotential of 241 mV to arrive at the benchmark current density (10 mA cm−2) with a remarkably small Tafel slope of 78.63 mV dec−1. It surpassed the state-of-the-art electrocatalyst for OER, that is, RuO2 (260 mV and 97.26 mV dec−1) in efficiency as well as instability. Density functional theory (DFT) calculations show that suitable Ni doping at the same time can increase the density of states of the Fermi level, resulting in excellent charge density and low intermediate adsorption energy. These discoveries provide a practical route for designing 2D polymetallic nanosheets to optimize catalytic OER performance.

Constructing hierarchical structure electrocatalyst for efficient hydrogen evolution and selective oxidation of benzylamine

Replacing oxygen evolution reaction (OER) with thermodynamically favorable oxidation reactions is a promising strategy to enhance the cathodic hydrogen production. In this paper, Mo doped CoNi metal-organic framework (MOF)-layered double hydroxide (LDH) nanosheet supported on Ni foam was constructed. The obtained MOF@LDH-Mo heterostructure array possessed large tangible surface area, rich active species and open electron transport channels, which was employed as electrocatalyst for benzylamine oxidation reaction (BOR) to replace OER for boosting hydrogen evolution. Benefitting from the unique structures, the MOF@LDH-Mo presented unprecedented intrinsic activity toward BOR, a high current density of 325 mA cm −2 can be reached at 1.7 V (vs RHE) in 1 mol·L −1 KOH solution. Meanwhile, the cell voltage decreased sharply, especially compared with that of overall water splitting (e.g. a reduction of 260 mV for the benchmark current density of 100 mA cm −2 ). Apart from H 2 production at cathode, value added chemical, benzonitrile, was yielded at anode with high Faradaic efficiency. This research provides an environmental friendly aqueous electrocatalytic route for production of valuable chemicals as well as green energy, hydrogen. The synthetic process of CoNi-MOF@LDH-Mo contains two steps. Firstly, CoNi-MOF nanoarrays were grown directly on nickel foam via hydrothermal process. Then, the CoNi-MOF@LDH-Mo was obtained by electro-depositing Mo-doped LDH on the surface of CoNi-MOF arrays.

Exposing Single Ni Atoms in Hollow S/N-Doped Carbon Macroporous Fibers for Highly Efficient Electrochemical Oxygen Evolution.

The development of efficient and cost-effective electrocatalysts toward the oxygen evolution reaction (OER) is highly desirable for clean energy and fuel conversion. Herein, the facile preparation of Ni single atoms embedded hollow S/N-doped carbon macroporous fibers (Ni SAs@S/N-CMF) as efficient catalysts for OER through pyrolysis of designed CdS-NiSx /polyacrylonitrile composite fibers is reported. Specifically, CdS provides the sulfur source for the doping of polyacrylonitrile-derived carbon matrix and simultaneously creates the hollow macroporous structure, while NiSx is first reduced to nanoparticles and finally evolves into single Ni atoms through the atom migration-trapping strategy. Benefiting from the abundantly exposed single Ni atoms and hollow macroporous structure, the resultant Ni SAs@S/N-CMF electrocatalysts deliver outstanding activity and stability for OER. Specifically, it needs an overpotential of 285mV to achieve the benchmark current density of 10mA cm-2 with a small Tafel slope of 50.8mV dec-1 .