泡沫镍基三维空心球CoFe_(2)O_(4)@NF复合材料的制备与析氧性能研究

为降低电解水阳极的析氧反应过电位,采用一步水热法制备了泡沫镍基钴铁混合氧化物(CoFe2O4@NF)复合材料。采用XRD、SEM、TEM和XPS等方法对复合材料进行表征,并利用三电极体系对其电解水析氧催化性能进行了测试。结果显示:Co Fe_(2)O_(4)以颗粒的形式聚集成空心球结构生长于泡沫镍基底上,其中空心球的直径大约4μm,而CoFe2O4的粒径约为40 nm左右。在1 mol·L^(-1)KOH溶液中,CoFe_(2)O_(4)@NF复合材料仅需293 mV的过电位即可达到20 m A·cm^(-2)的电流密度,Tafel斜率为51 m V·dec^(-1)。经过1000次循环伏安扫描和10 h电流时间曲线测试后,其析氧性能依旧保持高稳定性,在析氧催化材料领域有着广阔的研究前景。

Enhanced Oxygen Evolution Reaction Performance by Dynamic Adsorption of Intermediates on C2N-Supported Single Atom Catalysts

The dynamic adsorption of possible intermediates on single-atom catalysts(SACs)under working condition plays a key role in the electrocatalytic performance by the oxygen evolution reaction(OER),and therefore the performance of the dynamic adsorption should be fully considered in the theoretical screening of potential SACs.Based on density functional theory calculations,the OER performance of 27 types of C_(2)N-supported single transition metal atoms(TM@C_(2)N)is systematically investigated without and with considering the dynamic adsorption of possible intermediates.Without considering dynamic adsorption,only Rh@C_(2)N and Ni@C_(2)N are screened out as good catalysts.However,by further considering the dynamic adsorption configurations of possible intermediates,more promising TM@C_(2)N SACs including Fe(Co,Ni,Ru,Rh,Ir)@C_(2)N toward the OER are screened out.The presence of the intermediates(*HO,*O)on SACs could shift their d band center toward lower energy level,which makes the interaction between the adsorbate and SACs moderate and thus enhances their OER performance.The present work is instructive for further screening and designing of efficient single-atom catalysts for the oxygen evolution reaction.

Co_3O_4 supported on N,P-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions

Noble metals, such as platinum, ruthenium and iridium‐group metals, are often used as oxygen reduction or evolution reaction （ORR/OER） electrocatalysts. To reduce the cost and provide an application of bifunctional catalysis, in this work, cobalt oxide supported on nitrogen and phospho‐rus co‐doped carbon （Co3O4/NPC） was fabricated and examined as a bifunctional electrocatalyst for OER and ORR. To prepare Co3O4/NPC, NPC was pyrolyzed from melamine and phytic acid support‐ed on carbon, followed by the solvothermal synthesis of Co3O4 on NPC. Linear sweep voltammetry was used to evaluate the activity for OER and ORR. For OER, Co3O4/NPC showed an onset potential of 0.54 V （versus the saturated calomel electrode） and a current density of 21.95 mA/cm2 at 0.80 V, which was better than both Co3O4/C and NPC. The high activity of Co3O4/NPC was attributed to a synergistic effect of the N, P co‐dopants and Co3O4. For ORR, Co3O4/NPC exhibited an activity close to commercial Pt/C in terms of the diffusion limited current density （–4.49 vs–4.76 mA/cm2 at–0.80 V）, and Co3O4 played the key role for the catalysis. Chronoamperometry （current versus time） was used to evaluate the stability, which showed that Co3O4/NPC maintained 46%current after the chronoamperometry test for OER and 95% current for ORR. Overall, Co3O4/NPC exhibited high activity and improved stability for both OER and ORR.

Iridium‐containing water‐oxidation catalysts in acidic electrolyte

With the goal of constructing a carbon‐free energy cycle,proton‐exchange membrane(PEM)water electrolysis is a promising technology that can be integrated effectively with renewable energy resources to produce high‐purity hydrogen.IrO2,as a commercial electrocatalyst for the anode side of a PEM water electrolyzer,can both overcome the high corrosion conditions and exhibit efficient catalytic performance.However,the high consumption of Ir species cannot meet the sustainable development and economic requirements of this technology.Accordingly,it is necessary to understand the OER catalytic mechanisms for Ir species,further designing new types of low‐iridium catalysts with high activity and stability to replace IrO2.In this review,we first summarize the related catalytic mechanisms of the acidic oxygen evolution reaction(OER),and then provide general methods for measuring the catalytic performance of materials.Second,we present the structural evolution results of crystalline IrO2 and amorphous IrOx using in situ characterization techniques under catalytic conditions to understand the common catalytic characteristics of the materials and the possible factors affecting the structural evolution characteristics.Furthermore,we focus on three types of common low‐iridium catalysts,including heteroatom‐doped IrO2(IrOx)‐based catalysts,perovskite‐type iridium‐based catalysts,and pyrochlore‐type iridium‐based catalysts,and try to correlate the structural features with the intrinsic catalytic performance of materials.Finally,at the end of the review,we present the unresolved problems and challenges in this field in an attempt to develop effective strategies to further balance the catalytic activity and stability of materials under acidic OER catalytic conditions.

Defective high-entropy rocksalt oxide with enhanced metal‒oxygen covalency for electrocatalytic oxygen evolution

High‐entropy materials are emerging electrocatalysts by integrating five or more elements into one single crystallographic phase to optimize the electronic structures and geometric environments.Here,a rocksalt‐type high‐entropy oxide Mg_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2)Zn_(0.2)O(HEO)is developed as an electrocatalyst towards the oxygen evolution reaction(OER).The obtained HEO features abundant cation and oxygen vacancies originating from the lattice mismatch of neighboring metal ions,together with enlarged Co/Ni‒O covalency due to the introduction of less electronegative Mg and Zn.As a result,the HEO exhibits superior intrinsic OER activities,delivering a turnover frequency(TOF)15 and 84 folds that of CoO and NiO at 1.65 V,respectively.This study provides a mechanistic understanding of the enhanced OER on HEO and demonstrates the potential of high‐entropy strategy in developing efficient oxygen electrocatalysts by elaborately incorporating low‐cost elements with lower electronegativity.

Recent developments in metal phosphide and sulfide electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction(OER),as an important half‐reaction involved in water splitting,has been intensely studied since the last century.Transition metal phosphide and sulfide‐based compounds have attracted increasing attention as active OER catalysts due to their excellent physical and chemical characters,and massive efforts have been devoted to improving the phosphide and sulfide‐based materials with better activity and stability in recent years.In this review,the recent progress on phosphide and sulfide‐based OER electrocatalysts in terms of chemical properties,synthetic methodologies,catalytic performances evaluation and improvement strategy is reviewed.The most accepted reaction pathways as well as the thermodynamics and electrochemistry of the OER are firstly introduced in brief,followed by a summary of the recent research and optimization strategy of phosphide and sulfide‐based OER electrocatalysts.Finally,some mechanistic studies of the active phase of phosphide and sulfide‐based compounds are discussed to give insight into the nature of active catalytic sites.It is expected to indicate guidance for further improving the performances of phosphide and sulfide‐based OER electrocatalysts.

CoNiP/NC polyhedrons derived from cobalt-based zeolitic imidazolate frameworks as an active electrocatalyst for oxygen evolution

The oxygen evolution reaction(OER)plays an important role in the development of energy conversation and storage technologies including water splitting and metal-air batteries,where the development of electrocatalysts is paramount.In this study,cobalt-nickel phosphide/N-doped porous carbon polyhedron electrocatalysts(CoNiP/NC)were prepared by a facile two-step carbonization method and subsequent phosphorization calcination in an Ar atmosphere using cobalt-based zeolitic imidazolate frameworks(ZIFs)as precursors.Among the electrocatalysts obtained by controlling the carbonization and phosphorization temperature,the CoNiP/NC700 catalyst,where 700 refers to the calcination temperature(°C),exhibited superior electrocatalytic activity for the OER with an onset overpotential of approximate 220 mV and an overpotential of approximate 300 mV in alkaline solution at a current density of 10 mA/cm2.The CoNi/NC and Co/NC Samples were also tested for comparison and CoNiP/NC exhibited the better electrocatalytic activity at all the temperatures tested.The superior electrocatalytic activity of the phosphorization hybrid material can be attributed to the superior synergistic effect of Co,Ni,P and C due to their strong electron coupling interactions.The interconnected amorphous carbon anchored the active Co compounds to avoid aggregation and maintained conducting channels for electron transfer.The composite electrocatalyst prepared herein is a promising candidate for use in electrocatalytic OERs.

Efficient spinel iron‐cobalt oxide/nitrogen‐doped ordered mesoporous carbon catalyst for rechargeable zinc‐air batteries

A robust oxygen‐related electrocatalyst,composed of spinel iron‐cobalt oxide and nitrogen‐dopedordered mesoporous carbon(NOMC),was developed for rechargeable metal‐air batteries.Electrochemicaltests revealed that the optimal catalyst Fe_(0.5)Co/NOMC exhibits superior activity with ahalf‐wave potential of 0.89 V(vs.reversible hydrogen electrode)for the oxygen reduction reactionand an overpotential of 0.31 V at 10 mA cm^(−2)for the oxygen evolution reaction.For demonstration,the catalyst was used in the assembly of a rechargeable zinc‐air battery,which exhibited an exceptionallyhigh energy density of 820 Wh kg−1 at 100 mA cm^(−2),a high power density of 153 mW cm^(−2)at1.0 V,and superior cycling stability up to 432 cycles(144 h)under ambient air.

In situ formation of amorphous Fe-based bimetallic hydroxides from metal-organic frameworks as efficient oxygen evolution catalysts

Oxygen evolution from water driven by electrocatalysis or photocatalysis poses a significant challenge as it requires the use of efficient electro-/photo-catalysts to drive the four-electron oxygen evolution reaction(OER).Herein,we report the development of an effective strategy for the in situ chemical transformation of Fe-based bimetallic MIL-88 metal-organic frameworks(MOFs)into corresponding bimetallic hydroxides,which are composed of amorphous ultrasmall nanoparticles and afford an abundance of catalytically active sites.Optimized MOF-derived NiFe-OH-0.75 catalyst coated on glassy carbon electrodes achieved a current density of 10 mA cm^(-2)in the electrocatalytic OER with a small overpotential of 270 mV,which could be decreased to 235 mV when loading the catalysts on a nickel foam substrate.Moreover,these MOF-derived Fe-based bimetallic hydroxides can be used as efficient cocatalysts when combined with suitable photosensitizers for photocatalytic water oxidation.

An unusual network of α-MnO_(2) nanowires with structure-induced hydrophilicity and conductivity for improved electrocatalysis

Nanowires with anisotropic morphologies have been applied in various scientific and technological areas.It is also widely employed to fabricate nanowires into high-dimensional superstructures(arrays,networks etc.)to overcome the shortcomings of low-dimensional nanowires.However,typical strategies for constructing these superstructures are restricted to complicated and harsh synthetic conditions,not to mention unique 3D structures with advanced properties beyond common superstructures.Herein,we report an unusual network ofα-MnO_(2)nanowires with structure-induced hydrophilicity and conductivity.In the network,the nanowires are interconnected from all directions by nodes,and the 3D network structure is formed from the endless connection of nodes in a node-by-node way.The unique network structure brings about high hydrophilicity and conductivity,both of which are positive factors for an efficient electrocatalyst.Accordingly,the α-MnO_(2) network was tested for electrocatalytic water oxidation and showed significantly enhanced activity compared with isolatedα-MnO_(2)nanowires and 3Dα-MnO_(2)microspheres.This study not only provides a synthetic route toward an advanced network structure but also a new idea for the design of materials for electrochemistry with both efficient mass diffusion and charge transfer.

Robust MOF-253-derived N-doped carbon confinement of Pt single nanocrystal electrocatalysts for oxygen evolution reaction

Although carbon-supported platinum(Pt/C) is still considered the most active electrocatalyst for hydrogen evolution reaction(HER) and oxygen reduction reaction(ORR), its applications in metal–air batteries as a cathode catalyst, or for oxygen generation via water splitting electrolysis as an anode catalyst is mainly constrained by the insufficient kinetic activity and stability in the oxygen evolution reaction(OER). Here, MOF-253-derived nitrogen-doped carbon(N/C)-confined Pt single nanocrystals(Pt@N/C) have been synthesized and shown to be efficient catalysts for the OER. Even with low Pt mass loading of 6.1 wt%(Pt@N/C-10), the catalyst exhibits greatly improved activity and long-time stability as an efficient OER catalyst. Such high catalytic performance is attributed to the core-shell structure relationship, in which the active N-doped-C shell not only provides a protective shield to avoid rapid Pt nanocrystal oxidation at high potentials and inhibits the Pt migration and agglomeration, but also improves the conductivity and charge transfer kinetics.

Synergistic effect of metallic nickel and cobalt oxides with nitrogen-doped carbon nanospheres for highly efficient oxygen evolution

The most energy-inefficient step in the oxygen evolution reaction(OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co3O4 nanoparticles coupled with N-doped carbon hybrids(Ni/Co3O4@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co3O4 nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co3O4, and NC species, the obtained Ni/Co3O4@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 m V to afford 10 m A cm-2, lower Tafel slope of 52.27 m V dec-1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 m F cm-2 compared to those of unary Co3O4@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.

Fabrication of triangular Cu_(3)P nanorods on Cu nanosheets as electrocatalyst for boosted electrocatalytic water splitting

Non-precious electro catalysts with high-efficiency, cheapness and stablility are of great significance to replace noble metal electro catalysts in the hydrogen evolution reaction(HER) and oxygen evolution reaction(OER). In this work, triangular Cu@CuO nanorods on Cu nanosheets were fabricated by a novel in-situ oxidation approach using Cu nanosheets as self-template and conductive nano-substrate in an aqueous solution of NaOH/H2O2, and then by lowtemperature phosphorization treatments. The experimental results show that the phosphating temperature has a significant effect on the morphology, composition and number of active sites of Cu@Cu_(3)P nanorods. The Cu@Cu_(3)P-280 electrode exhibits a good HER catalytic activity of achieving a current density of 10 mA/cm^(2) at 252 mV in acid electrolyte. After catalysis for 14 h, the current density can still reach 72% of the initial value. Moreover, the Cu@Cu_(3)P-280 electrode also shows an excellent OER catalytic activity in basic electrolyte, reaching a current density of 10 mA/cm^(2) at the overpotential value of 200 mV. After catalysis for 12 h, the current density remained more than 93% of the initial value. This work provides a theoretical basis for the directional design and preparation of sustainable, low-cost, bifunctional electrocatalytic materials.

Cobalt/iron bimetal-organic frameworks as efficient electrocatalysts for the oxygen evolution reaction

The development of high efficiency and stable electrocatalysts for oxygen evolution is critical for energy storage and conversion systems. Herein, a series of Co/Fe bimetal-organic frameworks (MOFs) were fabricated using a facile ultrasonic method at room temperature, as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solution. The Co2Fe-MOF exhibited an overpotential of 280 mV at a current density of 10 mA cm^-2, a low Tafel slope of 44.7 mV dec^-1, and long-term stability over 12000 s in 1 mol L^-1 KOH. This impressive performance was attributed to the high charge transfer rate, large specific surface area, and synergistic effects of the cobalt and iron centers.

Proton reduction in the presence of oxygen by iron porphyrin enabled with 2nd sphere redox active ferrocenes

Hydrogen evolution in the presence of atmospheric level of oxygen is a significant barrier in the quest for an alternative,sustainable and green source of energy to counter the depleting fossil fuel sources and increasing global warming due to fossil fuel burning.Oxygen reduction is thermodynamically more favourable than proton reduction and it often produces reactive oxygenated species upon partial reduction which deactivates the catalyst.Thus,catalyst development is required for efficient proton reduction in the presence of oxygen.Here,we demonstrate an iron porphyrin having triazole containing 2nd sphere hydrogen bonding residues appended with redox active ferrocene moieties(α4-Tetra-2-(3-ferrocenyl-1,2,3-triazolyl)phenylporphyrin(FeFc4))as a bifunctional catalyst for fast and selective oxygen reduction to water and thus,preventing the proton reduction by the same catalyst from oxidative stress.Fe(0)is the active species for proton reduction in these iron porphyrin class of complexes and it is observed that the kinetics of proton reduction at Fe(0)state occurs at much faster rate than O2 reduction and thus,paving the way for selective proton reduction in the presence of oxygen.

Lanthanide-regulated oxygen evolution activity of face-sharing Ir〇6 dimers in 6H-perovskite electrocatalysts

The development of efficient oxygen evolution electrocatalysts with reduced noble metal uses is a critical challenge for the deployment of various advanced energy conversion technologies.Here,a series of lanthanide-contained 6H-perovskites with a formula of Ba3LnIr2〇9(Ln=lanthanides)are investigated as oxygen evolution electrocatalysts,whose active subunits(i.e.,face-sharing Ir〇6 dimers)can be regulated by the lanthanides in terms of catalytic activity.By using density functional theory(DFT)calculations,we establish the theoretical trend in activity for Ba3LnIr2〇96H-perovskites,the activity of which is correlated with the difference of adsorption free energy(△G〇-△Goh)between O*and OH*reaction intermediates.We further establish a volcano curve between△Go—△Goh and the calculated 0 p-band center Among the Ba3LnIr2〇96H-perovskites,Ba3Lalr2〇9 locates at the peak of volcano curve,and correspondingly is the most active electrocatalyst due to the optimal 0 p-band property.

Three-dimensional lily-like CoNi_2S_4 as an advanced bifunctional electrocatalyst for hydrogen and oxygen evolution reaction

Designing low-cost, highly efficient, and stable bifunctional electrocatalysts for both hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） is of vital significance for water splitting.Herein, three-dimensional lily-like CoNi_2S_4 supported on nickel foam（CoNi_2S_4/Ni） has been fabricated by sulfuration of the Co–Ni precursor. As expected, CoNi_2S_4/Ni possesses such outstanding electrocatalytic properties that it requires an overpotential of only 54 mV at 10 mA cm^（-2） and 328 mV at 100 mA cm^（-2） for HER and OER, respectively. Furthermore, by utilizing the CoNi_2S_4/Ni electrodes as bifunctional electrocatalysts for overall water splitting, a current density of 10 mA cm^（-2） can be obtained at a voltage of only 1.56 V.

In situ evolution of surface Co_(2)CrO_(4) to CoOOH/CrOOH by electrochemical method:Toward boosting electrocatalytic water oxidation

Developing non‐noble‐metal electrocatalyst with efficient and durable activity is a urgent task for addressing the sluggish reaction kinetics of electrochemical water oxidation.Structural evolution of the electrocatalyst is an important strategy for achieving enhanced performance.Herein,in situ evolution of surface Co_(2)CrO_(4) to CoOOH/CrOOH(CoOOH/CrOOH‐Co_(2)CrO_(4))by an electrochemical method under alkaline conditions was designed for enhancing the electrocatalytic performance of water oxidation.The experiments demonstrated that the synergy between CoOOH/CrOOH and Co_(2)CrO_(4) resulted in a marked increase in the number of active sites and improved the rate of charge transfer,which enhanced the activity for water oxidation.At a geometrical current density of 20 mA cm^(−2),the overpotential of the oxygen evolution reaction was 244 mV and the turnover frequency was 0.536 s^(−1) in 1.0 M NaOH.

Hierarchical cobalt phenylphosphonate nanothorn flowers for enhanced electrocatalytic water oxidation at neutral pH

Cobalt-based phosphate/phosphonates are a class of promising water oxidation catalysts at neutralpH.Herein,we reported a facile hydrothermal synthesis of various nanostructured cobalt phe-nylphosphonates.It is found that the number of hydroxyl group of structure-directing reagent iscrucial for the construction of 3D hierarchical structures including hierarchical nanosheet flow-er-like assemblies and nanothorn microsphere.These samples were characterized by scanningelectron microscopy,transmission electron microscopy,X-ray diffraction,infrared,and X-ray pho-toelectron spectroscopy techniques.They can act as highly efficient electrocatalysts for the oxygenevolution reaction at neutral pH.Among these,hierarchical cobalt phenylphosphonate nanothornflowers present excellent performance,affording a current density of 1 mA cm^-2 required a smalloverpotential of 393 mV.This work offers a new clue to develop high-performance metal phospho-nate/phosphate catalysts toward electrochemical water oxidation.

The role of proton dynamics on the catalyst-electrolyte interface in the oxygen evolution reaction

The development of non‐precious metal catalysts that facilitate the oxygen evolution reaction(OER)is important for the widespread application of hydrogen production by water splitting.Various perovskite oxides have been employed as active OER catalysts,however,the underlying mechanism that occurs at the catalyst‐electrolyte interface is still not well understood,prohibiting the design and preparation of advanced OER catalysts.Here,we report a systematic investigation into the effect of proton dynamics on the catalyst‐electrolyte interfaces of four perovskite catalysts:La_(0.5)Sr_(0.5)CoO_(3‐δ)(LSCO),LaCoO_(3),LaFeO_(3),and LaNiO_(3).The pH‐dependent OER activities,H/D kinetic isotope effect,and surface functionalization with phosphate anion groups were investigated to elucidate the role of proton dynamics in the rate‐limiting steps of the OER.For oxides with small charge‐transfer energies,such as LSCO and LaNiO_(3),non‐concerted proton‐coupled electron transfer steps are involved in the OER,and the activity is strongly controlled by the proton dynamics on the catalyst surface.The results demonstrate the important role of interfacial proton transfer in the OER mechanism,and suggest that proton dynamics at the interface should carefully be considered in the design of future high‐performance catalysts.