Electrocatalytic Materials Research Articles

HEXAMETHYLENETETRAMINE (C6H12N4) INDUCED HIGH-DENSITY NITROGEN DOPED REDUCED GRAPHENE: A NOVEL SONO-MICROWAVE ASSISTED SYNTHESIS AND CHARACTERIZATION TOWARDS RENEWABLE ENERGIES APPLICATIONS.

Development of low-cost electrocatalytic material for hydrogen evolution and oxygen reduction reaction (HER and ORR) is the main requirement for many renewable energies like the, Proton Exchange Membrane Fuel Cell (PEMFC) and Proton Exchange Membrane Electrolysers (PEME) Photo-electrochemical Water Splitting (PEWS) technologies. Herein, we report a novel, simple, economical and rapid one-pot Sono-microwave assisted synthesis of nitrogen doped graphene (NG) from graphene oxide in presence of a nitrogen precursor (Hexamethylenetetramine). The obtained NG was optimized by varying the ratio of GO to Hexamethylenetetramine to find the optimized N content in the catalyst and investigated as electrocatalyst for the ORR. Transmission electronic microscopy (TEM) and field emission scanning electronic microscopy (FE-SEM) micrograph of optimized NG showed well exfoliated graphene oxide with few layers of graphene while the X-ray photoelectron spectroscopy (XPS) depicts that about 11 % of nitrogen doping into the graphene lattice active forms of pyrrolic-N, pyridinic-N, and graphitic-N in 1:3NG catalyst is 55.00, 33.69, and 11.31 % respectively. Demonstrating the potential attributes of the Material in electrocatalytic renewable energy applications.

Tailoring of electrochemical properties on Nd-doped Ni3S2 electrode via doping strategy for supercapacitor application

Supercapacitor technology is a promising development in energy storage devices. Despite its potential as an anode material, nickel sulfhide (Ni3S2) utilization for practical application in energy storage devices is limited owing to its weak conductivity. Subsequently, it can be improved in the alteration of electronic properties by the introduction of impurities and surface defects. In this work, sulphur vacancy was created in hydrothermally synthesized nickel sulphide by inserting neodymium ions. The synergetic action of the dopant and produced sulphur vacancy have an effect on the electronic properties. The electrocatalytic behavior of the fabricated materials was also enhanced by adding polyethylene glycol, which was used as a reducing agent to promote the formation of sulphur vacancy. Examine the impact of neodymium doping concentration in nickel sulphide on the enhanced electrical structure of nickel sulphide by comparing electrocatalytic materials doped with varying amounts of neodymium. One of the 0.3-Nd doped nickel sulphide (0.3-NdNS) electrodes showed the best electronic properties, with a specific capacitance (Cs) of 2122.64 F g−1 at 1 A g−1 and energy density of 119.25 Wh Kg−1. The practical potential of the symmetric nature of 0.3-NdNS electrode material was examined with two electrode systems, exhibiting the specific capacitance (Cs). Our results suggest optimized 0.3-NdNS electrode materials have great potential for supercapacitor applications.

Perspectives on the development of highly active, stable, and cost‐effective OER electrocatalysts in acid

AbstractPolymer electrolyte membrane water electrolysis (PEMWE) is an attractive hydrogen energy production technology that offers various advantages such as compact design, high operating pressure, high current densities, and high hydrogen gas purity. However, PEMWE still faces several critical challenges, particularly with respect to the oxygen evolution reaction (OER) at the anode. Highly active, corrosion‐resistant electrocatalytic materials are required for the acidic OER owing to its sluggish kinetics involving four‐electron transfer under harsh anodic potentials. To date, IrO2‐ or RuO2‐based noble metal electrocatalysts have been employed as commercial acidic OER electrocatalysts for PEMWE. However, they remain inadequate in terms of satisfying the industrial activity/stability‐related requirements. Above all, the two noble metals are too rare and expensive, which significantly inhibits widespread commercialization of PEMWE. Therefore, low‐cost, highly active, and highly stable OER electrocatalysts that can operate in acidic media must be urgently developed. This review paper presents various state‐of‐the‐art strategies employed to address the aforementioned issues by classifying them according to objectives such as improving activity, enhancing stability, and reducing cost. Then, finally, we summarize major tasks and strategies to overcome them and put forward a few issues in this field.

Fruit waste-derived cellulose-templated hierarchical spheres of ultrathin MoS2 nanosheets for oxygen evolution reactions

Rising interest in cleaner and sustainable energy propelled interest in 2D nanostructured materials for energy conversion and storage technologies, including electrocatalytic materials for metal-air batteries and water-splitting devices. Oxygen evolution reactions are key constraints in many energy conversion applications because of their slow kinetics. The present work addressed fruit waste-derived cellulose-templated hierarchical spheres of ultrathin MoS2 (MoCe) nanosheets, synthesized via hydrothermal and lyophilization techniques, for oxygen evolution reactions. The pristine MoS2 and MoCe are thoroughly characterized by Raman, SEM, HRTEM, BET, FTIR, XRD, and XPS analyses to reveal their chemical, structural, morphological, and crystalline features. The quantity of cellulose used for the synthesis of MoCe governs the crystallite size and number of molecular lamellae in each MoS2 nanosheet, which in turn influences the electrocatalytic activity. The MoCe possesses ‘Craspedia’, a billy flower-like hierarchical microsphere comprising well-organized ultrathin MoS2 nanosheets and furnishes excellent mesoporosity with ample surface-active sites for electrocatalytic activity. A smaller Tafel slope (97 mV.dec-1) make cellulose-templated microspheres of ultrathin MoS2 nanosheets promising electrocatalysts for oxygen evolution reactions.

Edge-hosted CoFeB active sites with graphene nanosheets for highly selective nitrogen reduction reaction towards ambient ammonia synthesis

Electrocatalytic nitrogen reduction reaction (NRR) offers a suitable alternative to the conventional high energy intensive Haber–Bosch process for ambient ammonia (NH3) production without the release of greenhouse gases. Herein, a chemical reduction method is employed to effectively fabricate a hierarchical 3D nanostructure composed of CoFeB nanospheres precisely enveloped and interconnected with dynamically adaptable reduced graphene oxide (rGO) nanosheets for electrocatalytic NRR. Interconnected 3D CoFeB@ rGO nanostructures selectively reduced gaseous N2 to NH3 and demonstrated high Faradaic efficiency (31.6%) and NH3 yield rate (35 μg h−1 mg−1) at − 0.2 V in 0.05 M H2SO4, comparable to various state-of-the-art electrocatalytic materials for ambient NRR. Density functional theory (DFT) simulations additionally verify that interconnected CoFeB nanospheres with mechanically flexible graphene nanosheets are beneficial in lowering the energy threshold for N2 adsorption and successive protonation. First example of CoFeB@rGO heterostructures as electrocatalysts for high efficiency, pH-universal NRR to NH3 synthesis is highlighted in this study.

Fabrication and research of bi-functional CuNi2S4 nanosheets decorated TiO2/CuNi2S4 heterojunction photoanode for photoelectrochemical water splitting

As a traditional n-type semiconductor, TiO2 has good UV absorption ability and stable physical and chemical properties. However, its wide band gap and low oxygen evolution reaction (OER) activity limit its application in the field of photoelectrochemical (PEC) water splitting. In this work, a type-II TiO2/CuNi2S4 heterojunction photoanode is successfully constructed, which expanded the light absorption range to visible and enhanced the OER activity. Firstly, TiO2 nanotubes (NTs) thin films are prepared on Ti substrates by two-step anodization, and then the bi-functional electrocatalytic material CuNi2S4 is grown on TiO2 NTs in the shape of nanosheets (NSs) in situ by solvothermal method. As a bi-functional electrocatalytic material, CuNi2S4 has good visible light absorption property as well as OER catalytic activity. Compared with TiO2, the IPCE value of TiO2/CuNi2S4 is 2.59% at 635 nm, and that of TiO2 is a mere 0.002%. The separation efficiency and injection efficiency increase from 2.49% and 31.52% to 3.61% and 87.77%, respectively. At 1.23 V vs. RHE, the maximum photocurrent density is 0.26 mA/cm2, which is 2.6 times than that of TiO2 (0.11 mA/cm2), and can be maintained at 0.25 mA/cm2 for at least 2 h under light illumination. Moreover, a hydrogen production rate of 4.21 μmol⋅cm−2⋅h−1 is achieved within 2 h. This work provides a new idea for the application of TiO2 in the field of PEC water splitting and the construction of efficient and stable photoelectronic devices.

Construction of an Amethyst-like MoS2@Ni9S8/Co3S4 Rod Electrocatalyst for Overall Water Splitting.

Transition metal sulphide electrocatalytic materials possess the bright overall water-splitting performance of practical electrocatalytic technologies. In this study, an amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst was constructed via a one-step hydrothermal method with in-situ-grown ZIF-67 nanoparticles on nickel foam (NF) as a precursor. The rational design and synthesis of MoS2@Ni9S8/Co3S4 endow the catalyst with neat nanorods morphology and high conductivity. The MoS2@Ni9S8/Co3S4/NF with the amethyst-like rod structure exposes abundant active sites and displays fast electron-transfer capability. The resultant MoS2@Ni9S8/Co3S4/NF exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities, with low overpotentials of 81.24 mV (HER) at 10 mA cm-2 and 159.67 mV (OER) at 50 mA cm-2 in 1.0 M KOH solution. The full-cell voltage of overall water splitting only achieves 1.45 V at 10 mA cm-2. The successful preparation of the amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst provides a reliable reference for obtaining efficient electrocatalysts for overall water splitting.

Research progress of MOFs/carbon nanocomposites on promoting ORR in microbial fuel cell cathodes.

With the rapid development of the economy, energy demand is more urgent. Microbial fuel cells (MFCs) have the advantages of non-toxic, safety, and environmental protection, and are considered the ideal choice for the next generation of energy storage equipment. However, the slow kinetics of oxygen reduction reaction (ORR) on MFC air cathodes and the high cost of traditional platinum (Pt) catalysts hinder their practical application, so there is a need to develop efficient, low-cost, and stable electrocatalysts as alternatives. Recently, metal-organic framework (MOFs) has attracted wide attention in electrocatalysis. Electrocatalysts prepared by the nanocomposite of MOFs and carbon nanomaterials have multiple advantages, such as adjustable chemical properties, high specific surface area, and good electrical conductivity, which have been proven to be a promising electrocatalytic material. In this paper, the latest research progress of metal-organic frames (MOFs) and carbon nanocomposites is reviewed, and the preparation methods and modification of MOFs and carbon nanofibers, carbon nanotubes, and graphene composites are introduced, respectively, as well as their applications in MFC cathode. Finally, the main prospects of MOFs/carbon nanocomposite catalysts are put forward.

Hollow Starlike Ag/CoMo-LDH Heterojunction with a Tunable d-Band Center for Boosting Oxygen Evolution Reaction Electrocatalysis.

It is a challenging task to utilize efficient electrocatalytic metal hydroxide-based materials for the oxygen evolution reaction (OER) in order to produce clean hydrogen energy through water splitting, primarily due to the restricted availability of active sites and the undesirably high adsorption energies of oxygenated species. To address these challenges simultaneously, we intentionally engineer a hollow star-shaped Ag/CoMo-LDH heterostructure as a highly efficient electrocatalytic system. This design incorporates a considerable number of heterointerfaces between evenly dispersed Ag nanoparticles and CoMo-LDH nanosheets. The heterojunction materials have been prepared using self-assembly, in situ transformation, and spontaneous redox processes. The nanosheet-integrated hollow architecture can prevent active entities from agglomeration and facilitate mass transportation, enabling the constant exposure of active sites. Specifically, the powerful electronic interaction within the heterojunction can successfully regulate the Co3+/Co2+ ratio and the d-band center, resulting in rational optimization of the adsorption and desorption of the intermediates on the site. Benefiting from its well-defined multifunctional structures, the Ag0.4/CoMo-LDH with optimal Ag loading exhibits impressive OER activity, the overpotential being 290 mV to reach a 10 mA cm-2 current density. The present study sheds some new insights into the electron structure modulation of hollow heterostructures toward rationally designing electrocatalytic materials for the OER.

Bifunctional vanadium doped mesoporous Co3O4 on nickel foam towards highly efficient overall urea and water splitting in the alkaline electrolyte

Developing more active and stable electrode materials for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is necessary for electrocatalytic water and urea oxidation which can be used to generate hydrogen. Here, a low-cost vanadium-doped mesoporous cobalt oxide on Ni foam (V/meso-Co/NF) electrodes are obtained via the grouping of an in-situ citric acid (CA)-assisted evaporation-induced self-assembly (EISA) method and electrophoretic deposition process, and work as highly efficient and long-lasting electrocatalytic materials for OER/UOR. In particular, V/meso-Co/NF electrodes require 329 mV overpotential to maintain a 50 mA/cm2, with exceptional long-term durability of 30 h. Interestingly, V/meso-Co/NF also exhibits excellent electrocatalytic UOR performance, reaching 50 and 100 mA/cm2 versus RHE at low potentials of 1.34 and 1.35 V, respectively. By employing the V/meso-Co/NF materials as both the anode and cathode, this urea electrolysis assembly V/meso-Co/NF-5 (+,−) reaches current densities of 100 mA cm−2 at 1.62 V in KOH/urea, which is nearly 340 mV lesser than classical water electrolysis. The V/meso-Co/NF-5 electrocatalysts also exhibit remarkable durability for electrocatalytic OERs and UORs. The obtained findings revealed that the synthesized V/meso-Co/NF might be a promising electrode materials for overall urea-rich wastewater management and H2 generation from wastewater.

Efficient electrocatalytic two-electron oxygen reduction over aminophenol formaldehyde resin-derived carbon microspheres

The electrocatalytic 2-electron oxygen reduction reaction (2e-ORR) to hydrogen peroxide (H2O2) required cheap and efficient electrocatalytic materials. Herein cheap 3-aminophenol formaldehyde resin microspheres were synthesized at a large scale of about 15 g in one run. By annealing it, nitrogen-doped carbon spheres could be conveniently obtained, which was found to be efficient electrocatalyst for 2e-ORR with the highest H2O2 selectivity of about 94% at 0.4 V vs RHE. The electrolysis H2O2 production rate over N-doped carbon in 0.1 M KOH solution reached 48 mmol gcat-1h−1. Aminophenol formaldehyde resin-derived carbon provided a cheap and effective catalyst for electrocatalytic H2O2 production.

Amorphous nickel oxide electrodes with high-current-density electrocatalytic performance for hydrogen evolution

The widespread use of unsustainable fossil fuels has caused serious damage to the ecological environment. The development of sustainable clean energy is urgent. Producing hydrogen by water electrolysis can effectively solve fossil energy shortage and environmental pollution issues. The preparation of inexpensive, efficient, and stable electrocatalytic hydrogen evolution electrode materials is the key to achieving the application of electrocatalytic hydrogen evolution. Herein, the amorphous nickel oxide/nickel foam (NiOx/NF) hydrogen evolution electrode was prepared by a simple one-step hydrothermal method with hydrogen peroxide as an oxidant. The amorphous leaf array structure of NiOx/NF electrode can enrich the surface composition and expose more catalytic active sites. Further, hydrogen peroxide etching can optimize the electronic structure of NiOx, and accelerate the electron migration. Thus, NiOx/NF displays excellent alkaline hydrogen evolution activity with the low over potentials of 70, 318 and 361 mV at 10, 500 and 1000 mA cm−2, respectively, leading to high performance in alkaline HER than those of reported Ni-based electrodes and even surpasses commercial Pt/C at high current density. Our work provides a new approach for developing inexpensive electrocatalysts with excellent alkaline hydrogen evolution activity and stability.

Metal organic framework nanosheets in-situ derivatization of heterogeneous Cu2S/Ni3S2 nanoparticles for enhanced water splitting and glucose sensing

Metal organic frameworks (MOFs) are considered as promising electrocatalytic materials because of its good designability and structural diversity. Herein, the composite materials of Cu2S/Ni3S2@Ni-BDC/NF are successfully synthesized through the hydrothermal and electrodeposition methods. The distinctive heterostructure provides ample active sites and retains structural integrity to promote durability. When it is explored as bifunctional electrocatalyst, the overpotential of 63 mV at 10 mA cm−2 current density for the hydrogen evolution reaction (HER), the overpotential of 353 mV at 50 mA cm−2 current density for the oxygen evolution reaction (OER). In a two-electrode system, an extremely low cell voltage of 1.55 V is required to achieve 20 mA cm−2 current density. Moreover, Cu2S/Ni3S2@Ni-BDC exhibits satisfactory glucose sensitivity of 56,220 μA mM−1 cm−2 and outstanding anti-interference performance. This design not only successfully constructs 0D/2D heterogeneous interface of electrocatalyst, but also demonstrates the multifunctional application potential of water splitting and glucose electrochemical sensors.

Iron-Containing Nickel Cobalt Sulfides, Selenides, and Sulfoselenides as Active and Stable Electrocatalysts for the Oxygen Evolution Reaction in an Alkaline Solution

Iron-containing nickel sulfides, selenides, and sulfoselenides were synthesized via a simple two-step hydrothermal reaction (temperature ≤ 160 °C) for their application as electrocatalysts in the oxygen evolution reaction (OER) in an alkaline solution (1 mol L−1 KOH). The study demonstrated that iron-containing nickel cobalt sulfides and selenides exhibit superior OER performance with lower overpotentials compared to iron-free nickel cobalt sulfide and selenide, which highlights the significant role of iron in enhancing OER nickel cobalt electrocatalysts: Fe0.1Ni1.4Co2.9(S0.87O0.13)4, η50 = 318 mV; Fe0.2Ni1.5Co2.8(S0.9O0.1)4, η50 = 310 mV; Fe0.3Ni1.2Co2.5(S0.9O0.1)4, η50 = 294 mV; Fe0.6Ni1.2Co2.5(S0.83O0.17)4, η50 = 294 mV; Fe0.4Ni0.7Co1.6(Se0.81O0.19)4, η50 = 306 mV compared to Ni1.0Co2.1(S0.9O0.1)4, η50 = 346 mV; and Ni0.7Co1.4(Se0.85O0.15)4, η50 = 355 mV (all values at current densities η50 of 50 mA cm−2). Furthermore, the iron-containing nickel cobalt sulfoselenide Fe0.5Ni1.0Co2.0(S0.57Se0.25O0.18)4 displayed exceptional OER performance with η50 = 277 mV, surpassing the benchmark RuO2 electrode with η50 = 299 mV. The superior performance of the sulfoselenide was attributed to its low charge transfer resistance (Rct) of 0.8 Ω at 1.5 V vs. the reversible hydrogen electrode (RHE). Moreover, the sulfoselenide demonstrated remarkable stability, with only a minimal increase in overpotential (η50) from 277 mV to 279 mV after a 20 h chronopotentiometry test. These findings suggest that trimetallic iron, nickel and cobalt sulfide, selenide, and especially sulfoselenide materials hold promise as high-performance, cost-effective, and durable electrocatalysts for sustainable OER reactions. This study provides a valuable approach for the development of efficient electrocatalytic materials, contributing to the advancement of renewable energy technologies.

One-Dimensional Selenidostannates Based on an Infrequent Tetrameric Cluster [Sn4Se12] Exhibiting Electro-Catalytic Properties.

The discovery of low-cost and efficient electro-catalytic materials for hydrogen evolution reaction (HER) is very desirable in hydrogen energy technology. Here, a new type of one-dimensional (1-D) organic hybrid selenidostannate [Ni(en)3]n[Sn2Se5]n (SnSe-1, en = ethylenediamine) with an in situ [Ni(en)3]2+ complex was achieved by the solvothermal reaction of Sn, Se, and NiCl2·6H2O in a mixed solvent of en and triethanolamine at 160 °C for 10 days. The crystal structure of SnSe-1 contains a unique 1-D [Sn2Se52-]n chain built up from the sharing-edge connection of a hitherto-unknown tetrameric [Sn4Se12] cluster, which is separated by discrete [Ni(en)3]2+ complexes. SnSe-1 is first combined with Ni nanoparticles supported on conductive porous Ni foam (NF) to constitute a Ni/SnSe-1/NF electrode as the HER electro-catalyst, displaying superior electro-catalytic activity in near-neutral conditions.

NiB monolayer: A topological metal with high NORR electrocatalytic perfomance

Electrochemical reduction reaction of NO (NORR) offers a promising strategy for effective removal of NO coupled with synthesis of NH3. In this study, the newly reported NiB monolayer with topological metal properties is proved to have excellent catalytic activity and high selectivity toward NO-to-NH3 conversion by using density functional theory (DFT) and the constant potential method (CPM). Calculations reveal that the peculiar building blocks of Ni-B triangles and tetragons can facilitate NO adsorption and activation via an electron donation-back-donation interaction mechanism. The predicted free energy profiles of the four considered NORR pathways toward synthesis of NH3 are generally going downhill under the applied potential of 0 V, and an optimal reduction pathway was screened out with a maximum kinetic barrier of 0.16 eV during the hydrogenation process. The low adsorption free energy of H atom together with the existing relatively higher energy barriers for the formation of N2O/N2 guarantee the hydrogen evolution reaction (HER) and the partial reduction channel are less competitive than NH3 production. These findings enrich the potential application of two dimensional topological materials in electrocatalysis.

Carboxyl-functionalized carbon nanotubes coordinated with two-dimensional bimetallic porphyrin-based CuMOFs for efficient electrocatalytic CO2 reduction

The focus on electrocatalytic CO2 reduction to lessen surplus CO2 emissions and counteract the greenhouse effect has intensified. The synergistic combination of metal-organic frameworks (MOFs) and carbon-based materials has emerged as a potentially effective method to enhance electron transfer efficiency. In this study, we created a Cu-(Co+Cu)PMOF/CNT-COOH hybrid by integrating a two-dimensional bimetallic porphyrin-based CuMOF with carboxyl-modified carbon nanotubes. When compared with (Co+Cu)PMOF/CNT, which is formed through weak π-π interaction, our hybrid demonstrates superior stability, additional exposed active sites, and a higher electron transfer rate from CNT-COOH to Cu-(Co+Cu)PMOF, resulting in improved electrocatalytic action for CO2 reduction. Electrochemical tests indicate that the Cu-(Co+Cu)PMOF/CNT-COOH hybrid achieves a CO faradic efficiency of 95.98% with an impressive current density of -3.48 mA‧cm-2 at an overpotential of -0.9 V vs. RHE, significantly outperforming single metal porphyrin-based CuMOF counterparts. This research offers fresh perspective on how to thoughtfully construct high-performance electrocatalytic hybrid materials for CO2 reduction.

Facile eggplant assisted mixed metal oxide nanostructures: A promising electrocatalyst for water oxidation in alkaline media

In terms of efficiency and availability for electrochemical water splitting (EWS), producing electrocatalytic material for hydrogen (H2) fuel remains a difficulty. Furthermore, developing and producing low-cost, non-precious metal-based electrocatalysts for practical use is a global priority for researchers. Significant overpotential, low conductivity, and increased density are still factors to consider for alkaline water oxidation. We present here coprecipitated alumina (Al2O3) and eggplant-based cobalt oxide (Co3O4) nanostructures as electrocatalysts for the oxygen evolution reaction (OER). The as-prepared electrocatalyst offers active sites, enhanced electrical conductivity, and durability in the direction of OER. The desired electrocatalyst show lower overpotential value of 245 mV vs. a reversible hydrogen electrode (RHE) at a current density of 20 mA/cm2, a Tafel slope of 64 mV/dec, and stable electrochemical performance for 45 h as a result of a longer electrochemical activity. These findings suggest that this mixed metal oxide (nanostructures)-based electrocatalyst is a viable, active, and stable element for use in energy storage and conversion applications.

Size Effects of Highly Dispersed Bismuth Nanoparticles on Electrocatalytic Reduction of Carbon Dioxide to Formic Acid.

Electrocatalytic reduction of carbon dioxide into value-added chemical fuels is a promising way to achieve carbon neutrality. Bismuth-based materials have been considered as favorable electrocatalysts for converting carbon dioxide to formic acid. Moreover, size-dependent catalysis offers significant advantages in catalyzed heterogeneous chemical processes. However, the size effects of bismuth nanoparticles on formic acid production have not been fully explored. Here, we prepared Bi nanoparticles uniformly supported on porous TiO2 substrate electrocatalytic materials by in situ segregation of the Bi element from Bi4Ti3O12. The Bi-TiO2 electrocatalyst with Bi nanoparticles of 2.83 nm displays a Faradaic efficiency of greater than 90% over a wide potential range of 400 mV. Theoretical calculations have also demonstrated subtle electronic structural evolutions induced by the size variations of Bi nanoparticles, where the 2.83 nm Bi nanoparticles display the most active p-band and d-band centers to guarantee high electroactivity toward CO2RR.

A Self-Templated Design Approach toward Multivariate Metal-Organic Frameworks for Enhanced Oxygen Evolution.

Multivariate metal-organic framework (MOF) is an ideal electrocatalytic material due to the synergistic effect of multiple metal active sites. In this study, a series of ternary M-NiMOF (M = Co, Cu) through a simple self-templated strategy that the Co/Cu MOF isomorphically grows in situ on the surface of NiMOF is designed. Owing to the electron rearrange of adjacent metals, the ternary CoCu-NiMOFs demonstrate the improved intrinsic electrocatalytic activity. At optimized conditions, the ternary Co3 Cu-Ni2 MOFs nanosheets give the excellent oxygen evolution reaction (OER) performance of current density of 10mA cm-2 at low overpotential of 288mV with a Tafel slope of 87mV dec-1 , which is superior to that of bimetallic nanosheet and ternary microflowers. The low free energy change of potential-determining step identifies that the OER process is favorable at Cu-Co concerted sites along with strong synergistic effect of Ni nodes. Partially oxidized metal sites also reduce the electron density, thus accelerating the OER catalytic rate. The self-templated strategy provides a universal tool to design multivariate MOF electrocatalysts for highly efficient energy transduction.