Sulfur doped iron-nitrogen-hard carbon nanosheets as efficient and robust noble metal-free catalysts for oxygen reduction reaction in PEMFC

Transition metal-nitrogen-carbon(M-N-C)as a promising substitute for the conventional noble metalbased catalyst still suffers from low activity and durability for oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).To tackle the issue,herein,a new type of sulfur-doped ironnitrogen-hard carbon(S-Fe-N-HC)nanosheets with high activity and durability in acid media were developed by using a newly synthesized precursor of amide-based polymer with Fe ions based on copolymerizing two monomers of 2,5-thiophene dicarboxylic acid(TDA)as S source and 1,8-diaminonaphthalene(DAN)as N source via an amination reaction.The as-synthesized S-Fe-N-HC features highly dispersed atomic Fe Nxmoieties embedded into rich thiophene-S doped hard carbon nanosheets filled with highly twisted graphite-like microcrystals,which is distinguished from the majority of M-N-C with soft or graphitic carbon structures.These unique characteristics endow S-Fe-N-HC with high ORR activity and outstanding durability in 0.5 M H_(2)SO_(4).Its initial half-wave potential is 0.80 V and the corresponding loss is only 21 m V after 30,000 cycles.Meanwhile,its practical PEMFC performance is a maximum power output of 628.0 mW cm^(-2)and a slight power density loss is 83.0 m W cm^(-2)after 200-cycle practical operation.Additionally,theoretical calculation shows that the activity of Fe Nxmoieties on ORR can be further enhanced by sulfur doping at meta-site near FeN_(4)C.These results evidently demonstrate that the dual effect of hard carbon substrate and S doping derived from the precursor platform of amid-polymers can effectively enhance the activity and durability of Fe-N-C catalysts,providing a new guidance for developing advanced M-N-C catalysts for ORR.

Carbon Doping Triggered Efficient Electrochemical Hydrogen Evolution of Cross-Linked Porous Ru-MoO_(2) Via Solid-Phase Reaction Strategy

The defect-free structure of Mo-based materials is a“double-edged sword”,which endows the material with excellent stability,but limits its chemical versatility and application in electrochemical hydrogen evolution reaction(HER).Carbon doping engineering is an attractive strategy to effectively improve the performance of Mo-based catalyst and maintain their stability.Herein,we report a cross-linked porous carbon-doped MoO_(2)(C–MoO_(2))-based catalyst Ru/C–MoO_(2) for electrochemical HER,which is prepared by the convenient redox solid-phase reaction(SPR)of porous RuO_(2)/Mo_(2)C composite precursor.Theoretical studies reveal that due to the presence of carbon atoms,the electronic structure of C–MoO_(2) has been properly adjusted,and the loaded small Ru nanoparticles provide a fast water dissociation rate and moderate H adsorption strength.In electrochemical studies under a pH-universal environment,Ru/C–MoO_(2) electrocatalyst exhibits a low overpotential at a current density of 10 mA cm^(-2) and has a low Tafel slope.Meanwhile,Ru/C-MoO_(2) has excellent stability for more than 100 h at an initial current density of 100 mA cm^(-2).

Co-Ru alloy nanoparticles decorated onto two-dimensional nitrogen doped carbon nanosheets towards hydrogen/oxygen evolution reaction and oxygen reduction reaction

Constructing highly-efficient electrocatalysts toward hydrogen evolution reaction(HER)/oxygen evolution reaction(OER)/oxygen reduction reaction(ORR)with excellent stability is quite important for the development of renewable energy-related applications.Herein,Co-Ru based compounds supported on nitrogen doped two-dimensional(2D)carbon nanosheets(NCN)are developed via one step pyrolysis procedure(Co-Ru/NCN)for HER/ORR and following low-temperature oxidation process(Co-Ru@RuO_(x)/NCN)for OER.The specific 2D morphology guarantees abundant active sites exposure.Furthermore,the synergistic effects arising from the interaction between Co and Ru are crucial in enhancing the catalytic performance.Thus,the resulting Co-Ru/NCN shows remarkable electrocatalytic performance for HER(70 mV at 10 mA cm^(-2))in 1 M KOH and ORR(half-wave potential E_(1/2)=0.81 V)in 0.1 M KOH.Especially,the Co-Ru@RuO_(x)/NCN obtained by oxidation exhibits splendid OER performance in both acid(230 mV at 10 mA cm^(-2))and alkaline media(270 mV at 10 mA cm^(-2))coupled with excellent stability.Consequently,the fabricated two-electrode water-splitting device exhibits excellent performance in both acidic and alkaline environments.This research provides a promising avenue for the advancement of multifunctional nanomaterials.

MoNi_(4)-NiO heterojunction encapsulated in lignin-derived carbon for efficient hydrogen evolution reaction

Molybdenum nickel alloy has been proved to be an efficient noble-metal-free catalyst for hydrogen evolution reaction(HER) in alkaline medium, but its electrocatalytic activity and stability need to be further improved to meet industrial requirements. In this study, carboxymethylated enzymatic hydrolysis lignin(EHL) was used as a biomacromolecule frame to coordinate with transition metal ions and reduced by pyrolysis to obtain the MoNi_(4)-NiO heterojunction(MoNi_(4)-NiO/C). The oblate sphere structure of MoNi_(4)-NiO/C exposed a large catalytic active surface to the electrolyte. As a result, the hydrogen evolution reaction of MoNi_(4)-NiO/C displayed a low overpotentials of 41 mV to achieve 10 mA cm-2and excellent stability of 100 h at 100 mA cm^(-2)in 1 mol L^(-1)KOH, which was superior to that of commercial Pt/C. Lignin assisted the formation of NiO to construct the MoNi_(4)-NiO interface and MoNi_(4)-NiO heterojunction structure, which reduced the energy barrier by forming a more favorable transition states and then promoted the formation of adsorbed hydrogen at the heterojunction interface through water dissociation in alkaline media, leading to the rapid reaction kinetics. This work provided an effective strategy for improving the electrocatalytic performance of noble-metal-free electrocatalysts encapsulated by lignin-derived carbon.

Preparation of nitrogen and sulfur co-doped ultrathin graphitic carbon via annealing bagasse lignin as potential electrocatalyst towards oxygen reduction reaction in alkaline and acid media

Renewable lignin used for synthesizing materials has been proven to be highly potential in specific electrochemistry.Here,we report a simple method to synthesize nitrogen and sulfur co-doped carbon nanosheets by using bagasse lignin,denoted as lignin-derived carbon(LC).By adjusting the ratio of nitrogen source and annealing temperature,we obtained the ultrathin graphitic lignin carbon(LC-4-1000)with abundant wrinkles with high surface area of 1208 m2g_1 and large pore volume of 1.40 cm3g_1.In alkaline medium,LC-4-1000 has more positive half-wave potential and nearly current density compared to commercial Pt/C for oxygen reduction reaction(ORR).More importantly,LC-4-1000 also exhibits comparable activity and superior stability for ORR in acid medium due to its high graphitic N ratio and a direct four electron pathway for ORR.This study develops a cost-effective and highly efficient method to prepare biocarbon catalyst for ORR in fuel cells.

N/S co-doped 3D carbon framework prepared by a facile morphology-controlled solid-state pyrolysis method for oxygen reduction reaction in both acidic and alkaline media

Developing high-performance non-precious metal electrocatalysts for oxygen reduction reaction(ORR)is crucial for the commercialization of fuel cells and metal-air batteries.However,doped carbon-based materials only show good ORR activity in alkaline medium,and become less effective in acidic environment.We believe that an appropriate combination of both ionic and electronic transport path,and well dopant distribution of doped carbon-based materials would help to realize high ORR performance un-der both acidic and alkaline cond让ions.Accordingly,a nitrogen and sulfur co-doped carbon framework with hierarchical through-hole structure is fabricated by morphology-controlled solid-state pyrolysis of poly(aniline-co-2-ami no thiophenol)foam.The uniform high concentrations of nitrogen and sulfur,high intrinsic conductivity,and integrated three dimensional ionic and electronic transfer passageways of the 3D porous structure lead to synergistic effects in catalyzing ORR.As a result,the limiting current density of the carbonized poly(aniline-co-2-aminothiophenol)foam is equivalent to commercial Pt/C in acidic environment,and twice the latter in alkaline medium.

Differences in CO_(2)-Water-Rock Chemical Reactions among ’Sweet Spot’ Reservoirs:Implications for Carbon Sequestration

The Lucaogou Formation,located in the Jimsar Sag,Junggar Basin,NW China,has great potential for shale oil resources.In the process of CO_(2)-EOR(CO_(2) enhance oil recovery),mineral dissolution,precipitation and transformation,leading to the local corrosion or blockage of reservoirs,have a significant influence on recovery.In this study,a combination of high-temperature and high-pressure laboratory experiments and coupled temperature/fluid-chemistry multifield numerical simulations are used to investigate CO_(2)-water-rock reactions under various reservoir conditions in the upper and lower ’sweet spots’,to reveal the mechanisms underlying CO_(2)-induced mineral dissolution,precipitation and transformation.In addition,we quantitatively calculated the evolution of porosity over geological timescales;compared and analyzed the variability of CO_(2) transformation in the reservoir under a variety of temperature,lithology and solution conditions;and identified the main factors controlling CO_(2)-water-rock reactions,the types of mineral transformation occurring during long-term CO_(2) sequestration and effective carbon sequestration minerals.The results demonstrate that the main minerals undergoing dissolution under the influence of supercritical CO_(2) are feldspars,while the main minerals undergoing precipitation include carbonate rock minerals,clay minerals and quartz.Feldspar minerals,especially the initially abundant plagioclase in the formation,directly affects total carbon sequestration,feldspar-rich clastic rocks therefore having considerable sequestration potential.

Highly reactive and reusable heterogeneous activated carbons-based palladium catalysts for Suzuki-Miyaura reaction

Suzuki-Miyaura reaction of aryl halides with phenylboronic acid using a heterogeneous palladium catalyst based on activated carbons(AC) was systematically investigated in this work. Two different reaction modes(batch procedure and continuous-flow procedure) were used to study the variations of reaction processing. The heterogeneous catalysts presented excellent reactivity and recyclability for iodobenzene and bromobenzene substrates in batch mode, which can be attributed to stabilization of Pd nanoparticles by the thiol and amino groups on the AC supports. However, significant dehalogenation in the reaction mixture and Pd leaching from the heterogeneous catalysts were observed in continuous-flow mode.This unique phenomenon in continuous-flow mode resulted in a dramatic decline in reaction selectivity and durability of heterogeneous catalysts comparing with that of batch mode. In addition, the heterogeneous Pd catalysts with thiol-and amino-modified AC supports exhibited different reactivity and durability in batch and continuous-flow mode owing to the difference of interaction between Pd species and AC supports.

PtZn nanoparticles supported on porous nitrogen-doped carbon nanofibers as highly stable electrocatalysts for oxygen reduction reaction

The oxygen reduction reaction(ORR)electrocatalytic activity of Pt-based catalysts can be significantly improved by supporting Pt and its alloy nanoparticles(NPs)on a porous carbon support with large surface area.However,such catalysts are often obtained by constructing porous carbon support followed by depositing Pt and its alloy NPs inside the pores,in which the migration and agglomeration of Pt NPs are inevitable under harsh operating conditions owing to the relatively weak interaction between NPs and carbon support.Here we develop a facile electrospinning strategy to in-situ prepare small-sized PtZn NPs supported on porous nitrogen-doped carbon nanofibers.Electrochemical results demonstrate that the as-prepared PtZn alloy catalyst exhibits excellent initial ORR activity with a half-wave potential(E_(1/2))of 0.911 V versus reversible hydrogen electrode(vs.RHE)and enhanced durability with only decreasing 11 mV after 30,000 potential cycles,compared to a more significant drop of 24 mV in E_(1/2)of Pt/C catalysts(after 10,000 potential cycling).Such a desirable performance is ascribed to the created triple-phase reaction boundary assisted by the evaporation of Zn and strengthened interaction between nanoparticles and the carbon support,inhibiting the migration and aggregation of NPs during the ORR.

Roast Reaction of Bastinasite Concentrate Mixed with Sodium Carbonate

The research on the roast reaction mechanism of bastnasite concentrate mixture with Na 2CO 3 was carried out by means of thermal, X ray diffraction and chemical analyses. The isomorphous substitution, F -+Ce 3+ (Pr 3+ )→O 2- +Ce 4+ (Pr 4+ ), occurred and isomorphous mixed crystal, REO 1+x F 1-x (0< x <1), grew while roasting concentrate mixed with Na 2CO 3. REO 1+x F 1-x with different compositions were produced under different roasting conditions. It has been found that the lattice constant of REO 1+x F 1-x was a linear function of the content of fluorine: a 0=0 5499+0 00102 c F - (nm).

Performance evaluation of microemulsion acid for integrated acid fracturing in Middle Eastern carbonate reservoirs

Considering the characteristics of carbonate reservoirs in the Middle East,a low-viscosity microemulsion acid that can be prepared on site and has an appropriate retardation ability was developed.It was compared with four conventional acid systems(hydrochloric acid,gelled acid,emulsified acid and surfactant acid)through experiments of rotating disk,multistage acid fracturing and core flooding with CT scanning.The micro-etching characteristics and conductivity of fracture surfaces were clarified,and the variation of saturation field during water invasion and flowback of spent acid and the recovery of oil phase relative permeability were quantitatively evaluated.The study shows that the addition of negatively charged agent to the oil core of microemulsion acid can enhance its adsorption capacity on the limestone surface and significantly reduce the H+mass transfer rate.Moreover,the negatively charged oil core is immiscible with the Ca^(2+)salt,so that the microemulsion acid can keep an overall structure not be damaged by Ca^(2+)salt generated during reaction,with adjustable adsorption capacity and stable microemulsion structure.With high vertical permeability along the fracture walls,the microemulsion acid can penetrate into deep fracture wall to form network etching,which helps greatly improve the permeability of reservoirs around the fractures and keep a high conductivity under a high closure pressure.The spent microemulsion acid is miscible with crude oil to form microemulsion.The microemulsion,oil and water are in a nearly miscible state,with basically no water block and low flowback resistance,the flowback of spent acid and the relative permeability of oil are recovered to a high degree.

Binary molten salt in situ synthesis of sandwich-structure hybrids of hollowβ-Mo2C nanotubes and N-doped carbon nanosheets for hydrogen evolution reaction

Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water.Herein,a sandwich composite structure(designed as MS-Mo2C@NCNS)ofβ-Mo2C hollow nanotubes(HNT)and N-doped carbon nanosheets(NCNS)is designed and prepared using a binary NaCl–KCl molten salt(MS)strategy for HER.The temperature-dominant Kirkendall formation mechanism is tentatively proposed for such a three-dimensional hierarchical framework.Due to its attractive structure and componential synergism,MS-Mo2C@NCNS exposes more effective active sites,confers robust structural stability,and shows significant electrocatalytic activity/stability in HER,with a current density of 10 mA cm-2 and an overpotential of only 98 mV in 1 M KOH.Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS,leading to enhanced electronic transport and suitable adsorption free energies of H*(ΔGH*)on the surface of electroactive Mo2C.More significantly,the MS-assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non-noble metal electrocatalysts toward efficient hydrogen evolution.

Catalytic effect of alkali carbonates on CO_2 gasification of Pingshuo coal

Na2CO3,Li2CO3,and K2CO3 were used as additives to Pingshuo(PS) coal that was subsequently gasified under a CO2 stream.The catalytic gasification of coal samples by CO2 in the presence single or mixed alkali carbonates was investigated by thermogravimetric analysis.The experimental results indicate that the catalytic effect of Li2CO3 is significantly larger than that of Na2CO3 or K2CO3.The catalytic effect of the mixed,bi-metal carbonate containing Li2CO3 and Na2CO3,or Li2CO3,and K2CO3,is related to the composition of the catalyst and the proportion of the two components.The bi-metal carbonates having a mole ratio of 9:1(Li:X) has the largest catalytic effect for PS coal gasification.A synergistic effect between Li and K,or Na,carbonate appears at temperatures greater than 1300 K.An un-reacted shrinking core model is suitable for kinetic analysis of catalytic gasification of coal samples in the presence of alkali carbonates.It is inappropriate,however,to evaluate the catalytic effect only by the activation energy obtained from the kinetic calculations.

A comprehensive overview of the electrochemical mechanisms in emerging alkali metal-carbon dioxide batteries

Alkali metal-carbon dioxide(Li/Na/K-CO_(2))batteries are emerging electrochemical energy storage technologies in the context of the energy crisis and the urgent demand for carbon neutrality.Alkali metal-CO_(2) batteries offer a new strategy for CO_(2) fixation and utilization,and thus has been receiving considerable attention in recent years.Considerable progress has been achieved since alkali metal-CO_(2) batteries were invented,especially in terms of development of new electrode materials,and yet,research is lacking on the underlying mechanisms of the systems.This is the first typical review focusing on the electrochemical mechanisms of metal-CO_(2) batteries that summarizes the current understanding of and provides insights into the thermodynamic reaction pathways,the kinetic characteristics,and the crucial factors determining the reaction mechanisms in alkali metal-CO_(2) batteries.The review starts with the fundamental concepts of alkali metal-CO_(2) batteries,followed by a comprehensive discussion of the working mechanisms on cathodes and anodes.Moreover,the operation mechanisms of state-of-the-art electrolytes,including liquid and(quasi-)solid-state electrolytes,are also described.Finally,we identify the unsolved problems in current alkali metal-CO_(2) batteries and propose potential topics for future research.

Study on Direct Synthesis of Diphenyl Carbonate with Heterogeneous Catalytic Reaction (V) Screening Catalysts and Optimizing Synthesis Conditions

Pd/LaxPbyMnOz, Pd/C, Pd/molecular sieve and Pd-heteropoly acid catalysts for direct synthesis of diphenyl carbonate (DPC) by heterogeneous catalytic reaction were compared and the results of DPC synthesis indicated that the catalyst Pd/LaxPbyMnOz had higher activity. The Pd/LaxPbyMnOz catalyst and the support was characterized by XRD, SEM and TEM, the main phase was La0.62Pb0.38MnO3 and the average diameter could be about 25.4 nm. The optimum conditions for synthesis of DPC with Pd/LaxPbyMnOz were determined by orthogonal experiments and the experimental results showed that reaction temperature was the first factor of effect on the selectivity and yield of DPC, and the concentration of O2 in gas phase also had significant effect on selectivity of DPC. The optimum reaction conditions were catMyst/phenol mass ratio 1 to 50, pressure 4.5 MPa,volume concentration of O2 25%, reaction temperature 60° and reaction time 4 h. The maximum yield and average selectivity could reach 13% and 97% respectively in the batch operation.

Green and Effective Ammonium Carbonate-assisted Process for Drying Hemicellulose Obtained through Alkali Extraction of Bleached Bamboo Kraft Pulp

Hemicellulose has a wide range of applications,including that as an emulsifier for the food industry and raw material for the synthesis of bioethanol/biochemicals and biodegradable films.Hemicellulose is usually present as a spent liquor,such as the prehydrolysis liquor of the prehydrolysis kraft dissolving pulp production process and the alkali extraction liquor of the cold caustic extraction of pulp fibers.Due to its dilute nature,hemicellulose needs to be dried for practical utilization,and this is challenging.In this study,cellulose and hemicellulose in a bleached bamboo kraft pulp were separated using an alkali extraction process.Hemicellulose obtained from the extraction liquor was dried by an ammonium carbonate-assisted drying process.The effects of drying time and drying temperature were determined.Structure of the hemicellulose obtained by the ammonium carbonate-assisted drying process was similar to that of original hemicellulose,as revealed by detailed Fourier transform infrared and X-ray diffraction analyses.The novel drying method was more energy efficient and required a shorter drying time than the conventional freeze drying method,and the excellent solubility in alkaline solutions favored the chemical modification of hemicellulose.The dried hemicellulose can be used as a renewable raw material for the preparation of hydrogels and other substances such as bioethanol/biochemicals and biodegradable films.

The First Report of Thermochemical Sulfate Reduction Reaction in the Upper Paleozoic Carbonate Rocks of Southeastern Ordos Basin

Thermochemical sulfate reduction （TSR） is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce H2S and CO2. TSR has been studied in many sedimentary basins such as China＇s Sichuan and Tarim basins because it has a profound impact on the commercial viability of petroleum resources, with HzS typically being undesirable.

Recent Advances in Mechanistic Understanding of Metal-Free Carbon Thermocatalysis and Electrocatalysis with Model Molecules

Metal-free carbon,as the most representative heterogeneous metal-free catalysts,have received considerable interests in electro-and thermo-catalytic reac-tions due to their impressive performance and sustainability.Over the past decade,well-designed carbon catalysts with tunable structures and heteroatom groups coupled with various characterization techniques have proposed numerous reaction mechanisms.However,active sites,key intermediate species,precise structure-activity relationships and dynamic evolution processes of carbon catalysts are still rife with controversies due to the monotony and limitation of used experimental methods.In this Review,we sum-marize the extensive efforts on model catalysts since the 2000s,particularly in the past decade,to overcome the influences of material and structure limitations in metal-free carbon catalysis.Using both nanomolecule model and bulk model,the real contribution of each alien species,defect and edge configuration to a series of fundamentally important reactions,such as thermocatalytic reactions,electrocatalytic reactions,were systematically studied.Combined with in situ techniques,isotope labeling and size control,the detailed reaction mechanisms,the precise 2D structure-activity relationships and the rate-determining steps were revealed at a molecular level.Furthermore,the outlook of model carbon catalysis has also been proposed in this work.

Atomically dispersed Mn-Nx catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction(ORR).Although rarely studied,Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis.Here,we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets(MnNCS)from an Mn-hexamine coordination framework.The atomically dispersed Mn-N4 sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure.The optimized MnNCS displayed an excellent ORR performance in half-cells(0.89 V vs.reversible hydrogen electrode(RHE)in base and 0.76 V vs.RHE in acid in half-wave potential)and Zn-air batteries(233 mW cm^(−2)in peak power density),along with significantly enhanced stability.Density functional theory calculations further corroborated that the Mn-N4-C1_(2)site has favorable adsorption of*OH as the rate-determining step.These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.

Hollow ZIF-67-derived Co@N-doped carbon nanotubes boosting the hydrogenation of phenolic compounds to alcohols

The selective hydrogenation of highly toxic phenolic compounds to generate alcohols with thermal stability,environmental friendliness,and non-toxicity is of great importance.Herein,a series of Co-based catalysts,named Co@NCNTs,were designed and constructed by direct pyrolysis of hollow ZIF-67(HZIF-67)under H_(2)/Ar atmosphere.The evolution of the catalyst surface from the shell layer assembled by ZIF-67-derived particles to the in situ-grown hollow nitrogen-doped carbon nanotubes(NCNTs)with certain length and density is achieved by adjusting the pyrolysis atmosphere and temperature.Due to the synergistic effects of in situ-formed hollow NCNTs,well-dispersed Co nanoparticles,and intact carbon matrix,the as-prepared Co@NCNTs-0.10-450 catalyst exhibits superior catalytic performance in the hydrogenation of phenolic compounds to alcohols.The turnover frequency value of Co@NCNTs-0.10-450is 3.52 h^(-1),5.9 times higher than that of Co@NCNTs-0.40-450 and 4.5 times higher than that of Co@NCNTs-0.10-550,exceeding most previously reported non-noble metal catalysts.Our findings provide new insights into the development of non-precious metal,efficient,and cost-effective metal-organic framework-derived catalysts for the hydrogenation of phenolic compounds to alcohols.