Enhanced water splitting through different substituted cobalt-salophen electrocatalysts

Synthesis of stable catalysts for water splitting is important for the renewable and clean energy production. Here, water oxidation activities of cobalt (II) complexes CoL¹-CoL³ (1–3) with salophen type ligands (N,N′-bis(salicylidene)-4-chloro-1,2-phenylendiamine (H₂L¹), N,N′-bis(salicylidene)-4-bromo-1,2-phenylendiamine (H₂L²) and N,N′-bis(salicylidene)-4-nitro-1,2-phenylendiamine (H₂L³)) are studied by electrochemical techniques, FE-SEM images and XRD patterns. Linear sweep voltammetry studies indicate that 2 and 3 have superior activities and only require the overpotential of 316 and 247 mV vs. RHE at current density of 10 mA/cm² with Tafel slopes of 75 and 50 mVdec^?1 at pH = 11. Experiments show relationships between the stability of the complexes and their catalytic activity. It is revealed that substituents on ligands affect the catalytic behaviors. Experiments show that in the presence of 2 and 3, the complexed cobalt ions are likely candidates as molecular catalysts for water oxidation. It is speculated that the O–O bond formation occurs by oxidizing the active center of cobalt complexes.     

Benzimidazole Schiff base copper(II) complexes as catalysts for environmental and energy applications: VOC oxidation,oxygen reduction and water splitting reactions

The new copper(II) complexes [Cu(μ-1κO:2κONN′-HL1)(μ-1κO:2κO′-NO₃)]₂.[Cu(μ-1κO:2κONN′-HL1)(CH₃OH)]₂(NO₃)₂ (1) and [Cu(κONN′-HL2)(μ-1κOO’:2κO′-NO₃)]_n (2), derived from the new pro-ligands H₂L1 = 2-(5,6-dihydroindolo[1,2-c]quinazolin-6-yl)-5-methylphenol and H₂L2 = 2-(5,6-dihydroindolo[1,2-c]quinazolin-6-yl)-4-nitrophenol, were synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and their structural features were unveiled by single-crystal X-ray diffraction analysis. This discloses a dimeric structure for 1 and a polymeric infinite 1D metal-organic chain for 2. The complexes were evaluated as catalysts for the oxidation of toluene, a volatile organic compound (VOC), and for oxygen reduction and water splitting reactions. 1 exhibits a higher activity for the peroxidative conversion of toluene to oxygenated products (total yields up to 38%), whereas 2 demonstrates a superior performance for electrochemical energy conversion applications, i.e., for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline medium in terms of higher ORR current densities, lower Tafel slope (73 mV dec^?1) and higher number of electrons exchanged (3.9), comparable to that of commercial Pt/C. Complex 2 also shows a better performance with lower onset potential and higher current densities for both OER and HER when studied as electrocatalyst for water splitting.     

Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

Heteroleptic thiolate diamine nickel complexes: Noble-free-metal catalysts in electrocatalytic and light-driven hydrogen evolution reaction

Three mononuclear heteroleptic nickel complexes bearing the non-innocent o-aminobenzenethiolate (2-amnt) ligand and different diamine ligands, namely, [Ni(2-amnt)(o-phen)] (o-phen = o-phenylenediamine) (1), [Ni(2-amnt)(3,4-daba)] (3,4-daba = 3, 4-diamino benzoic acid) (2) and [Ni(2-amnt)(dmnt)] (dmnt = diaminomaleonitrile) (3), were synthesized and characterized. Complexes 1–3 are active homogeneous proton reduction electrocatalysts in dimethylformamide with trifluoroacetic acid as a proton source. All the three complexes are tested in light-driven hydrogen evolution reaction, indicating different catalytic efficiencies. Thus, although complex 3 indicates no catalytic action, both complexes 1 and 2 catalyze H₂ evolution in water-dimethylformamide solutions using fluorescein (Fl) as a photosensitizer. Complex 2 acts as a homogeneous catalyst reached 834 turnovers (TON); whereas 1, despite being active in hydrogen evolution reaction (HER), decomposes to form nanomaterials. DFT calculations combined with electrochemical and spectroscopic data were employed to investigate the catalytic mechanism for H₂ formation as well as to unravel the key factors that influence the relative catalytic efficiencies. The proposed catalytic pathway involves ligand-based reduction and protonation steps followed by the formation of a nickel-hydride intermediate that reacts with a solution proton to generate H₂ via a very low energy transition state.     

Thermal thiocyanate ligand substitution kinetics of the solar cell dye N719 by acetonitrile, 3-methoxypropionitrile, and 4-tert-butylpyridine

The kinetics of the thiocyanate substitution of the solar cell sensitizer [Ru(Hdcbpy)₂(NCS)₂]²⁻, 2(n-C₄H₉)₄N⁺ (H₂dcbpy=L=2,2′-bipyridine-4,4′-dicarboxylic acid), known as N719, by acetonitrile, 3-methoxypropionitrile, and 4-tert-butylpyridine (4-TBP) have been determined in both homogenous solutions and colloidal mixtures of N719-dyed TiO₂ nanocrystalline particles. Thiocyanate ligand substitution by the solvents (S) acetonitrile or 3-methoxypropionitrile in homogeneous solutions occurs at elevated temperatures (80–110 °C) by means of a simple slow pseudo-first-order reaction leading to the formation of the product [RuL₂(NCS)(S)]⁺ with a half-life time t_1/2 2000 h of N719 at 80 °C. If tert-butylpyridine (0.5 M) is added, the end product instead becomes [RuL₂(NCS)(4-TBP)]⁺ with a t_1/2 1000 h. When N719 is bound to TiO₂ particles, the reactions with S and 4-TBP give the same products as occur in the homogenous solutions; however, the reactions are approximately 10 times faster. For the reaction of a colloidal mixture of N719-dyed TiO₂ particles in acetonitrile containing 0.5 M 4-TBP, a t_1/2(het) of 120 h was calculated at 85 °C. The N719-based DSSC cells with acetonitrile and 4-TBP as solvent and additive are therefore not expected to be able to pass a 1000-h thermal stress test in the dark at 85 °C due to thermal degradation of the N719 dye. Adding guanidine thiocyanate to the colloidal solutions, however, decreased the rate of [RuL₂(NCS)(4-TBP)]⁺ formation by a factor of 2–10; it thus may be used as an additive to prevent the thermal degradation of thiocyanate-based ruthenium complexes in DSSC solar cells.     

Mercury(II)-complex with 5-methyl-1,3,4-thiadiazole-2-thiol: kinetic studies of hydrogen storage

Mixed ligand mercury(II) complexes of 2-meracpto-5-methyl-1,3,4-thiazdiazole (HmtzS) and phosphines or diamines having the general formulae [Hg(mtsZ)₂(diphos)] {diphos = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppe), 1,1′-bis(diphenylphosphino)ferrocene (dppf)}, [Hg(mtsZ)₂(PPh₃)₂] and [Hg(mtsZ)₂(diamine)] {diamine = bipyridyl (Bipy) or 1,10-phenthroline (Phen), were successfully synthesized by simple mixing method. The complexes were characterized by elemental analysis, molar conductivity, IR and NMR (¹H, ¹³C and ³¹P) spectroscopic methods. The mtzS^? ligand was coordinated through the sulfur atom of thiol group, whereas the diphosphine or diamine ligands bonded as bidentate chelating ligand to afford tetrahedral environment around the Hg(II) ions. Moreover, the complex [Hg(mtsZ)₂] was used in order to study its ability to store hydrogen. The results of hydrogen isotherm at different temperatures prove that [Hg(mtsZ)₂] was able to store 0.8 wt% at a pressure of 80 bar 77 K. Furthermore, the kinetic study of hydrogen storage was studied and the kinetic study was carried out using the Langmuir. Moreover, the adsorption kinetic results revealed that hydrogen storage in [Hg(mtsZ)₂] follow the pseudo-second-order model with coefficient regression equal to 0.99.     

Proton reduction using cyclopentadienyl Fe(II) (benzene-1,2-dithiolato) carbonyl complexes as electrocatalysts

The UV photolysis of cyclopentadienyl iron dicarbonyl dimer [CpFe(CO)₂]₂ and benzene-1,2-dithiol or 3,6-dichloro-1,2-benzenedithiol afforded dinuclear iron complexes [Cp₂Fe₂(CO)(bdt)(μ-CO)] (1) and [Cp₂Fe₂(CO)(Cl₂-bdt)(μ-CO)] (2) respectively (bdt = benzene-1,2-dithiolato, Cl₂-bdt = dichloro-1,2-benzenedithiolato). Further oxidation of the two complexes resulted in the release of CO and generated [CpFe(bdt)]₂ (3) and [CpFe(Cl₂-bdt)]₂ (4). All four complexes were found to catalyse proton reduction at a similar overpotential and rate when trifluoroacetic acid (TFA) was used as a proton source. Both experimental and computational studies lent support to a mononuclear iron intermediate species carrying the CpFe(bdt) or CpFe(Cl₂-bdt) moiety acting as the catalyst in the proton reduction process.     

Tailoring morphological and chemical properties of covalent triazine frameworks for dual CO2 and H2 adsorption

The development of functional porous samples suitable as gas-adsorption materials is a key challenge of modern materials chemistry to face with global warming or issues related to renewable energy-storage solutions. Herein, a set of five Covalent Triazine Frameworks (CTFs) featured by high specific surface area (SSA, up to 3201 m² g^?1) and N content as high as 12.2 wt% have been prepared through a rational synthetic strategy and exploited with respect to their gas uptake properties. Among CTFs from this series, CTF-pDCB/DCI^HT (4) combines ideal morphological and chemico-physical properties for CO₂ and H₂ adsorption. Noteworthy, besides ranking among CTFs with the highest CO₂ adsorption capacity reported so far (up to 5.38 mmol g^?1 at 273 K and 1 bar), 4 displays a H₂ excess uptake at 77 K of 2.84 and 5.0 wt% at 1 and 20 bar, respectively, outperforming all CTF materials and 2D Porous Organic Polymers of the state-of-the-art.     

Reorganization of a photosensitive carbo-benzene layer in a triptych nanocatalyst with enhancement of the photocatalytic hydrogen production from water

The preparation of a triptych nanomaterial made of TiO₂ nanoparticles as semiconductor, Ag plasmonic nanoparticles and a carbo-benzene macrocyclic molecule as photosensitizer is described, and used to produce hydrogen by photo-reduction of pure deionized water under 2.2 bar argon pressure without any electrical input. Silver nanoparticles (~5 nm) are grafted onto the surface of commercial TiO₂ nanoparticles (~23 nm) by a photo-deposition process using an original silver amidinate precursor. The thickness of the photosensitive layer (2 nm), which completes the assembly, plays a crucial role in the efficiency and robustness of the triptych nanocatalyst. Thanks to the organic layer reorganization during the first ~24 h of irradiation, it leads to an enhancement of the hydrogen production rate up to 5 times. The amount of silver and carbo-benzene are optimized, along with the mass concentration of nanocatalyst in water and the pH of the aqueous medium, to allow reaching a hydrogen production rate of 22.1 μmol·h⁻¹·g_{photocatalyst}⁻¹.     

Dysprosium doped copper oxide (Cu1-xDyxO) nanoparticles enabled bifunctional electrode for overall water splitting

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu_1-xDy_xO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu_1-xDy_xO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm^?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm^?2 and relatively high current density of 66 mAcm^?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm^?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.     

Organic photosensitizers containing fused indole-imidazole ancillary acceptor with triphenylamine donor moieties for efficient dye-sensitized solar cells

Controlling the morphology of sensitizer on a TiO₂ nanocrystalline surface is beneficial to facilitating electron injection and suppressing charge recombination. Given that the N,N-dimethylaniline-substituted imidazole-fused-indole on the middle segment for preventing π aggregation can deteriorate its intrinsic photostability, we incorporate a promising building block of fused-indole-imidazole [(1,4-dihydroimidazo[4,5-b]indole) DHII)] ring as the additional acceptor to construct a novel TD₂, TD₃ and YD₃ with D–(A)π-D, D–(DA₂)π-D, D–π-D(A)-π-D architecture, which exhibits several characteristics: (i) possible chelation of imidazole ring (through N) to the titanium ions on the TiO₂ surface which can assist in increasing the electron injection into the conduction band of photoanode, (ii) showing a moderate electron-withdrawing capability for an ideal push-pull balance in both promising photocurrent and photovoltage; (iii) endowing an ideal morphology control with strong capability of restraining the intermolecular aggregation and facilitating the formation of a compact sensitizer layer via N,N-dimethylaniline groups grafted onto the fused-indole-imidazole unit. The co-adsorbent-free dye-sensitized solar cell (DSSC) based on dye TD₃ exhibits very promising conversion efficiency as high as 6.04 ± 0.01%, with a short-circuit current density (J_sc) of 13.57 mA cm^?2, an open-circuit voltage (V_oc) of 0.80 V, and a fill factor (FF) of 0.774 under AM 1.5 illumination (100 mW cm^?2). TD₃-based device showed better performance because of the two anchoring groups, which play a significant role for better adsorption on the TiO₂ surface along with the enhanced kinetics of photoexcited electron injection.     

Gas and vapor adsorption in octacyanometallate-based frameworks Mn2[M(CN)8] (M = W,Mo) with exposed Mn sites

Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn₂M(CN)₈·7H₂O (M = Mo, 1·7H₂O; W, 2·7H₂O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)₈]⁴⁻ units are linked via octahedral Mn²⁺ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H₂O, N₂ and H₂) measurements. H₂ adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading ΔH_ads has the value of ca. 10.0 kJ mol⁻¹ for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn²⁺ sites left exposed by the removal of coordinated water molecules in the structure.     

Hydrogen evolution by photocatalytic decomposition of water under ultraviolet–visible irradiation over K2La2Ti3−xMxO10+δ perovskite

New layered transition metal substituted perovskite-type oxides K₂La₂Ti_3−xM_xO_10+δ (M = Fe, Ni, W; δ varies with different M) were synthesized with high-temperature solid state reaction, and characterized with X-ray diffraction (XRD) and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS). The photocatalytic activity of these catalysts was studied under ultraviolet and visible light irradiation. The results indicated that substitution of a part of Ti⁴⁺ with Fe³⁺ and W⁶⁺ resulted in a marked increase in water splitting activity. The activity of these catalysts for water splitting decreased in the order: Fe³⁺ > W⁶⁺ > Ni²⁺ ≥ no substitution. The effect of different amounts of Ti⁴⁺ with Fe³⁺ substitution on water splitting was also evaluated. The highest hydrogen evolution was observed for perovskite composition having a Fe:Ti molar ratio of 1:14 (1:12 weight ratio) and this hydrogen evolution was over 4 times higher than the Fe-free K₂La₂Ti₃O₁₀ composition. Fe was also found to be a promising component for photo activity under visible light irradiation. Finally, the effect of Na₂S/Na₂SO₃ system as the sacrificial agent on the photocatalytic activity was also studied.     

Theoretical exploration of the mechanisms on the iron complexes catalyzed ammonia borane dehydrogenation and polyaminoborane formation

Density functional theory study was carried out to provide mechanistic insights into the bifunctional iron complex [Fe(DCPE)(PhNCH₂)₂ (DCPE = 1,2-bis(dicyclohexylphosphino)ethane)] catalyzed AB dehydrogenation and polyaminoborane formation with the detailed mechanistic pathways. Computational results imply a favorable scenario that complies with a proton transfer pathway between the metal center and ligand, which could further lead to a kinetically feasible transition state with low energy barrier. Subsequent polyaminoborane formation involves the generation of nucleophiles, and the NH₂BH₂ moiety, which is featured with a nitrogen lone pair, plays a crucial role in the chain polyaminoborane formation. Natural bond orbital analysis (NBO), and energy decomposition analysis (EDA) were utilized to study the orbital interactions and intramolecular weak interactions were revealed by the independent gradient model based on Hirshfeld partition method (IGMH).     

Novel mixed ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) with 1,10-phenanthroline and acesulfame. Synthesis,structural analysis and hydrogen adsorption study

Four novel metal organic framework (MOF) structures containing acesulfame (ace) and 1,10-phenanthroline (phen) ligands of Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ metal cations were synthesized. The crystal structure analysis of three compounds (1, 2, and 3) was also performed. The structural formula for complex 4 is proposed based on spectroscopic and thermal analysis data. It has been determined that structures 1, 2, and 4 are in a distorted octahedral geometry. It has been suggested that the charge balance of the coordination sphere with 2+ is provided by two monoanionic ace ligands located outside the coordination sphere as counter-ion. In structure 3, there are two Cu^II metal cations, two phen ligands coordinated as bidentate to each metal cation and ace ligand that provides monoanionic-monodentate coordination. The Cu²⁺ cation has distorted bipyramidal geometry. The maximum hydrogen gas adsorption has been found 1.4575 mL/g (0.046 wt%) for the Ni complex.     

Studies on electrochemical properties of thionyl chloride reduction by Schiff base metal(II) complexes

Electrocatalytic effects associated with the reduction of thionyl chloride in a LiAlCl₄–SOCl₂ electrolyte solution containing Schiff base metal(II) (metal (M): Co, Ni, Cu and Mn) complexes are evaluated by determining the kinetic parameters for the reactions using cyclic voltammetry at a glassy carbon electrode. The charge-transfer process during the reduction of thionyl chloride is affected by the concentration of the catalyst. Catalytic effects are demonstrated from both a shift in the reduction potential for the thionyl chloride in a more positive direction and an increase in peak currents. The reduction of thionyl chloride is diffusion controlled. Catalytic effects are larger for thionyl chloride solutions containing M(II)(1,5-bis(salicylidene imino) pentane) (M(II)(SALPE)) rather than M(II)(1,3-bis(salicylidene imino) propane) (M(II)(SALPR)). Significant improvements in cell performance are found in terms of the both thermodynamics and kinetic parameters for the thionyl chloride reduction. An exchange rate constant, k⁰, of 1.89×10⁻⁸ cm s⁻¹ is found at the bare electrode, while larger values of 2.79×10⁻⁸ to 2.09×10⁻⁶ cm s⁻¹ are observed in the case of the catalyst-supported glassy carbon electrode.     

A mild H3BO3 environment for water splitting

A weakly acidic H₃BO₃ solution (pH = 5.1) was used to synthesize new oxygen-evolution catalysts for water splitting under mild conditions. Two novel oxygen-evolution catalysts, Co–BA_i and Mn–BA_i (BA_i = inorganic boric acid), were obtained in the H₃BO₃ solution with added Co²⁺ and Mn²⁺, respectively. The average oxygen evolution rate in the H₃BO₃ solution with Co²⁺ was 0.3133 μmol/h, about 70 times greater than the rate without a metal ion; the rate with Mn²⁺ was 1.13 μmol/h, about 250 times greater. The phases, morphologies, and compositions of the Co–BA_i and Mn–BA_i catalysts were analysed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy.     

Density functional studies on the hydrogen storage capacity of boranes and alanes based cages

The hydrogen storage (H-storage) capacity of various boranes and alanes have been investigated using density functional theory (DFT) based M05-2X method employing 6–31+G** basis set. The changes in the H-storage capacities of borane and alane upon substitution of antipodal atoms in the cages by C, Si, and N have also been investigated. It is found from the calculations that a maximum of 20 H₂ molecules can be adsorbed on the deltahedron faces of these cages. The maximum gravimetric density has been observed for boranes when compared to alanes. The H-storage capacity of closo-borane dianion [B₁₂H₁₂]²⁻, monocarborane [CB₁₁H₁₂]¹⁻, dicarborane [C₂B₁₀H₁₂], and closo-azaborane [NB₁₁H₁₂] cages is almost similar (∼22 wt.%). Among these cages, B_BB dianion show higher binding energy (BE) and BE per H₂ molecule (BE/nH₂) which are 181.06 and 9.03 kJ/mol, respectively. In the case of alanes, dicarbalane [C₂Al₁₀H₁₂] has maximum H-storage capacity of 11.6 wt.%. Based on these findings, a new MOF with carborane (MOF-5_CC) as linker has been designed. The calculation on the new MOF-5B_CC reveals that it has H-storage capacity of 6.4 wt.% with BE/nH₂ of 3.02 kJ/mol.     

Carbon fiber supported Co/Co3O4-embedded N-doped carbon microparticles for efficient overall seawater splitting and oxygen reduction

Due to low cost and abundance, direct seawater splitting to produce hydrogen is an encouraging strategy to alleviate the consumption of fossil energy, while also avoiding freshwater stress. However, when natural seawater is utilized as the electrolyte, the catalysts on the cathode and anode of water splitting should not only have high activity to promote energy efficiency, but also have good stability and durability to resist the corrosion of chloride ions. Herein, a hierarchical carbon-based catalyst for hydrogen and oxygen evolution, ZIF-67/CF-1, was prepared by annealing a composite of ZIF-67 and carbon fiber (CF). It exhibits good electrocatalytic activity and stability for overall splitting in natural seawater and neutral PBS solution. Impressively, when an electrolyzer consisting of ZIF-67/CF-1||ZIF-67/CF-1 is applied to overall seawater splitting, the current density of 10 mA/cm² is achieved with a drive voltage of 2.46 V, which is only 0.28 V higher than precious metal-based electrolyzer (Pt/C||IrO₂). Meanwhile, ZIF-67/CF-1 shows outstanding catalytic ability for oxygen reduction (E_1/2 = 0.84 V, Tafel slope = 66.9 mV/dec), also demonstrating its application potential in rechargeable batteries and fuel cells.     

Ultrasmall Mo2C in N-doped carbon material from bimetallic ZnMo-MOF for efficient hydrogen evolution

The exploration and development of cost-effective and highly stable electrocatalysts with the highest possible energy efficiency remain a constant pursuit in the catalyst design and synthesis for electrocatalytic hydrogen evolution reaction (HER). In this work, a convenient approach is proposed to synthesize a type of ultrafine Mo₂C nanoparticles in average sizes of 3–4 nm embedded in hierarchically porous N-doped carbon material calcined from bimetallic ZnMo-MI (MI = 2-methylimidazole) is obtained at 1000 °C, denoted as ZnMo-MI-1000. First of all, the crystalline hybrid metal-organic framework of ZnMo-MI is fabricated from zeolitic imidazolate framework of Zn-MI precursors via solvothermal reaction, in which the conversion from Zn-MI to ZnMo-MI occurs gradually over time. After calcination, the as-obtained ZnMo-MI-1000 sample shows a satisfying HER performance with the small overpotential of 83.0 mV in 0.5 M H₂SO₄ and 100.1 mV in 1.0 M KOH to reach a current density of 10 mA cm^?2, which is attributed to ultrasmall Mo₂C, Mo and N-doped graphitic carbon matrix. The multiporous network of ZnMo-MI-1000 can provide continuous mass transportation with a minimal diffusion resistance that produce effective electrocatalytic kinetics in both acidic and alkaline media, which is utilized as a highly active and durable nonprecious metal electrocatalyst for HER.