Noble Metal-based Electrocatalysts Research Articles

Carbon aerogel supported Ni–Fe catalysts for superior oxygen evolution reaction activity

AbstractElectrochemical water splitting presents an optimal approach for generating hydrogen (H2), a highly promising alternative energy source. Nevertheless, the slow kinetics of the electrochemical oxygen evolution reaction (OER) and the exorbitant cost, limited availability, and susceptibility to oxidation of noble metal-based electrocatalysts have compelled scientists to investigate cost-effective and efficient electrocatalysts. Bimetallic nanostructured materials have been demonstrated to exhibit improved catalytic performances for the oxygen evolution reaction (OER). Herein, we report carbon aerogel (CA) decorated with different molar ratios of Fe and Ni with enhanced OER activity. Microwave irradiation was involved as a novel strategy during the synthesis process. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Energy dispersive X-ray spectroscopy (EDAX spectra and EDAX mapping), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HR-TEM), and Selected Area Electron Diffraction (SAED) were used for physical characterizations of as-prepared material. Electrochemical potential towards OER was examined through cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). The FeNi/CA with optimized molar ratios exhibits low overpotential 377 mV at 10 mAcm−2, smaller Tafel slope (94.5 mV dec−1), and high turnover frequency (1.09 s−1 at 300 mV). Other electrocatalytic parameters were also calculated and compared with previously reported OER catalysts. Additionally, chronoamperometric studies confirmed excellent electrochemical stability, as the OER activity shows minimal change even after a stability test lasting 3600 s. Moreover, the bimetallic (Fe and Ni) carbon aerogel exhibits faster catalytic kinetics and higher conductivity than the monometallic (Fe), which was observed through EIS investigation. This research opens up possibilities for utilizing bi- or multi-metallic anchored carbon aerogel with high conductivities and exceptional electrocatalytic performances in electrochemical energy conversion.

Breaking Highly Ordered PtPbBi Intermetallic with Disordered Amorphous Phase for Boosting Electrocatalytic Hydrogen Evolution and Alcohol Oxidation.

Constructing amorphous/intermetallic (A/IMC) heterophase structures by breaking the highly ordered IMC phase with disordered amorphous phase is an effective way to improve the electrocatalytic performance of noble metal-based IMC electrocatalysts because of the optimized electronic structure and abundant heterophase boundaries as active sites. In this study, we report the synthesis of ultrathin A/IMC PtPbBi nanosheets (NSs) for boosting hydrogen evolution reaction (HER) and alcohol oxidation reactions. The resulting A/IMC PtPbBi NSs exhibit a remarkably low overpotential of only 25 mV at 10 mA cm-2 for the HER in an acidic electrolyte, together with outstanding stability for 100 h. In addition, the PtPbBi NSs show high mass activities for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR), which are 13.2 and 14.5 times higher than those of commercial Pt/C, respectively. Density functional theory calculations demonstrate that the synergistic effect of amorphous/intermetallic components and multimetallic composition facilitate the electron transfer from the catalyst to key intermediates, thus improving the catalytic activity of MOR. This work establishes a novel pathway for the synthesis of heterophase two-dimensional nanomaterials with high electrocatalytic performance across a wide range of electrochemical applications.

Acidic Oxygen Evolution Reaction: Fundamental Understanding and Electrocatalysts Design.

Water electrolysis driven by "green electricity" is an ideal technology to realize energy conversion and store renewable energy into hydrogen. With the development of proton exchange membrane (PEM), water electrolysis in acidic media suitable for many situations with an outstanding advantage of high gas purity has attracted significant attention. Compared with hydrogen evolution reaction (HER) in water electrolysis, oxygen evolution reaction (OER) is a kinetic sluggish process that needs a higher overpotential. Especially in acidic media, OER process poses higher requirements for the electrocatalysts, such as high efficiency, high stability and low costs. This review focuses on the acidic OER electrocatalysis, reaction mechanisms, and critical parameters used to evaluate performance. Especially the modification strategies applied in the design and construction of new-type electrocatalysts are also summarized. The characteristics of traditional noble metal-based electrocatalysts and the noble metal-free electrocatalysts developed in recent decades are compared and discussed. Finally, the current challenges for the most promising acidic OER electrocatalysts are presented, together with a perspective for future water electrolysis.

Ru/Ir-Based Electrocatalysts for Oxygen Evolution Reaction in Acidic Conditions: From Mechanisms, Optimizations to Challenges.

The generation of green hydrogen by water splitting is identified as a key strategic energy technology, and proton exchange membrane water electrolysis (PEMWE) is one of the desirable technologies for converting renewable energy sources into hydrogen. However, the harsh anode environment of PEMWE and the oxygen evolution reaction (OER) involving four-electron transfer result in a large overpotential, which limits the overall efficiency of hydrogen production, and thus efficient electrocatalysts are needed to overcome the high overpotential and slow kinetic process. In recent years, noble metal-based electrocatalysts (e.g., Ru/Ir-based metal/oxide electrocatalysts) have received much attention due to their unique catalytic properties, and have already become the dominant electrocatalysts for the acidic OER process and are applied in commercial PEMWE devices. However, these noble metal-based electrocatalysts still face the thorny problem of conflicting performance and cost. In this review, first, noble metal Ru/Ir-based OER electrocatalysts are briefly classified according to their forms of existence, and the OER catalytic mechanisms are outlined. Then, the focus is on summarizing the improvement strategies of Ru/Ir-based OER electrocatalysts with respect to their activity and stability over recent years. Finally, the challenges and development prospects of noble metal-based OER electrocatalysts are discussed.

Pulse potential mediated selectivity for the electrocatalytic oxidation of glycerol to glyceric acid

Preventing the deactivation of noble metal-based catalysts due to self-oxidation and poisonous adsorption is a significant challenge in organic electro-oxidation. In this study, we employ a pulsed potential electrolysis strategy for the selective electrocatalytic oxidation of glycerol to glyceric acid over a Pt-based catalyst. In situ Fourier-transform infrared spectroscopy, quasi-in situ X-ray photoelectron spectroscopy, and finite element simulations reveal that the pulsed potential could tailor the catalyst’s oxidation and surface micro-environment. This prevents the overaccumulation of poisoning intermediate species and frees up active sites for the re-adsorption of OH adsorbate and glycerol. The pulsed potential electrolysis strategy results in a higher glyceric acid selectivity (81.8%) than constant-potential electrocatalysis with 0.7 VRHE (37.8%). This work offers an efficient strategy to mitigate the deactivation of noble metal-based electrocatalysts.

Development of metal free biochar based material for water electrolysis hydrogen production using anion exchange membrane: Creating circular economy

In recent days, a steady growth is being noted in hydrogen energy field owing to the global rise in population and increased energy demand. Fast depletion of fossil-based fuels and climate change issues are driving nations towards exploring an alternate energy resource. Hydrogen energy is one such an option owing to availability of simple and cost intensive technology involvement. Alkaline water electrolysis is one of the simplest ways of producing hydrogen utilizing renewable energy and oxygen as the only byproduct thus not contributing to carbon footprint. However, immediate attention is needed to minimize the cost of electrolyzer components, maintenance and energy. Commercial proton exchange membrane water electrolyzers (PEM) in market employ large capital cost due to high-priced Nafion and other PFSA membranes, titanium endplates and noble metal-based electrocatalysts. As a consequence, researchers are looking into the usage of Anionic exchange membrane (AEM) for water/alkali based electrolyzer for producing hydrogen with non-noble metal electrocatalysts and low-cost metal end plates. In this article a waste coconut shell derived biochar is explored as the carbon matrix for base of electrocatalysts to replace other high-cost carbon support for electrocatalyst in water electrolyzer. The structural and electrical properties of the coconut shell biochar are studied and compared with other available carbon supports. To deep drive in the electrolyzer performance this approach is further extended to MEA (Membrane Electrode Assembly) level to study the metal free electrocatalyst behavior in real-time environmental conditions.

MAX Phase (Nb4 AlC3 ) For Electrocatalysis Applications.

In search for novel materials to replace noble metal-based electrocatalysts in electrochemical energy conversion and storage devices, special attention is given to a distinct class of materials, MAX phase that combines advantages of ceramic and metallic properties. Herein, Nb4 AlC3 MAX phase is prepared by a solid-state mixing reaction and characterized morphologically and structurally by transmission and scanning electron microscopy with energy-dispersive X-ray spectroscopy, nitrogen-sorption, X-ray diffraction analysis, X-ray photoelectron and Raman spectroscopy. Electrochemical performance of Nb4 AlC3 in terms of capacitance as well as for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is evaluated in different electrolytes. The specific capacitance Cs of 66.4, 55.0, and 46.0 F g-1 at 5mV s-1 is determined for acidic, neutral and alkaline medium, respectively. Continuous cycling reveals high capacitance retention in three electrolyte media; moreover, increase of capacitance is observed in acidic and neutral media. The electrochemical impedance spectroscopyshowed a low charge transfer resistance of 64.76 Ω cm2 that resulted in better performance for HER in acidic medium (Tafel slope of 60mV dec-1 ). In alkaline media, the charge storage value in the double layer is 360 mF cm-2 (0.7V versus reversible hydrogen electrode) and the best ORR performance of the Nb4 AlC3 is achieved in this medium (Tafel slope of 126mV dec-1 ).

The Impact of Operando Analysis in the Understanding of Oxygen Evolution Reaction Ranging from Intrinsic to Technical Scales

The development of state of the art and cost-effective catalyst materials for the sluggish oxygen evolution reaction (OER) is of paramount importance for realizing practical water electrolysis for green hydrogen production. Crucial for this endeavor is the determination of the OER mechanism and a better understanding of all these background processes that affect catalyst activity and stability. Thus, to further elucidate all these processes operando characterization techniques performed dynamically during OER are used as powerful tools which allow monitoring of key reaction intermediates, active sites, charge transfer and material transformation coupled processes etc. In this work we summarize our recent investigations covering noble and 3d transition metal-based OER electrocatalysts by different operando techniques and we show the importance of such techniques in the unraveling catalyst activation/deactivation mechanisms. Thus, our efforts are ranging from half-cell characterization of electrocatalyst intrinsic properties to single-cell analysis of phenomena occurring during their technical operation.Operando techniques like eQCM, XAS, ICP-OES and single cell testing will be presented aiming to emphasize on the critical role of operando in the understanding of fundamental aspects of electrochemistry [1], like intrinsic catalyst properties (Fig. 1a), the effect of electrolyte impurities such as Fe (Fig. 1b-d) on Ni-based electrocatalysts in alkaline environment [2] as well as mechanistic phenomena taking place during catalyst activation (Fig. 1e-f) leading to the formation of the active sites for OER in acidic environment [3].

A Doping-Induced SrCo0.4Fe0.6O3/CoFe2O4 Nanocomposite for Efficient Oxygen Evolution in Alkaline Media.

Perovskite and spinel oxides are promising alternatives to noble metal-based electrocatalysts for oxygen evolution reaction (OER). Herein, a novel perovskite/spinel nanocomposite comprised of SrCo0.4Fe0.6O3 and CoFe2O4 (SCF/CF) is prepared through a simple one-step method that incorporates iron doping into a SrCoO3- δ matrix, circumventing complex fabrication processes typical of these materials. At a Fe dopant content of 60%, the CoFe2O4 spinel phase is directly precipitated from the parent SrCo0.4Fe0.6O3 perovskite phase and the number of active B-site metals (Co/Fe) in the parent SCF can be maximized. This nanocomposite exhibits a remarkable OER activity in alkaline media with a small overpotentional of 294mV at 10mAcm-2. According to surface states analysis, the parent SCF perovskite remains in its pristine form under alkaline OER conditions, serving as a stable substrate, while the second spinel CF is covered by 5/8 monolayer (ML) O*, exhibiting considerable affinity toward the oxygen species involved in the OER. Analysis based on advanced OER microkinetic volcano model indicates that a 5/8 ML O* covered-CF is the origin for the remarkable activity of this nanocomposite. The results reported here significantly advance knowledge in OER and can boost application, scale-up and commercialisation of electrocatalytic technologies toward clean energy devices.

Electronic structure optimizing of Ru nanoclusters via Co single atom and N, S co-doped reduced graphene oxide for accelerating water electrolysis

The development of efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is impending for the advancement of water-splitting. In this study, we developed a novel electrocatalyst consisting of highly dispersed Ru nanoclusters ameliorated by cobalt single atoms and N, S co-doped reduced graphene oxide (CoSARuNC@NSG). Benefitted from the optimized electronic structure of the Ru nanoclusters induced by the adjacent single atomic Co and N, S co-doped RGO support, the electrocatalyst exhibits exceptional HER performance with overpotentials of 15 mV and 74 mV for achieving a current density of 10 mA cm−2 in alkaline and acidic water. The catalyst outperforms most noble metal-based HER electrocatalysts. Furthermore, the electrolyzer assembled with CoSARuNC@NSG and RuO2 demonstrated an overall voltage of 1.56 V at 10 mA cm−2 and an excellent operational stability for over 25 h with almost no attenuation. Theoretical calculations also deduce its high HER activity demonstrated by the smaller reaction energy barrier due to the optimized electronic structure of Ru nanoclusters. This strategy involving the regulation of metal nanoparticles activity through flexible single atom and GO support could provide valuable insights into the design of high-performance and low-cost HER catalysts.

Iron substitution enabled lattice oxygen oxidation and cation leaching for promoting surface reconstruction in electrocatalytic oxygen evolution

The low-cost transition metal oxides have drawn widespread interest as alternatives to noble metal-based electrocatalysts for oxygen evolution reaction (OER). Transition metal oxides usually undergo surface reconstruction during electrochemical reaction to form the actual active species. However, in-depth understanding and regulating of the surface reconstruction of active phases for oxides in OER remains an onerous challenge. Herein, we report a simple Fe element substitution strategy to facilitate the surface reconstruction of spinel oxide NiCr2O4 to generate active (oxy)hydroxides. The activated Fe-doped NiCr2O4 (Act-Fe-NCO) exhibits a lower OER overpotential of 259 mV at 10 mA cm−2 than activated NiCr2O4 (Act-NCO, 428 mV), and shows excellent stability for 120 h. The electrochemically activated CV measurement and nanostructure characterizations reveal that Fe substitution could promote the consumption of lattice oxygen during electrochemical activation to induce the leaching of soluble Cr cations, thereby facilitating the reconstruction of remaining Ni cations on the surface into (oxy)hydroxide active species. Moreover, theoretical calculations further demonstrate that the O 2p band center of NiCr2O4 moves towards the Fermi level due to Fe substitution, thus promoting lattice oxygen oxidation and providing greater structural flexibility for surface reconstruction. This work shows a promising way to regulate the surface reconstruction kinetics and OER electrocatalytic activity of transition metal oxides.

Influence of boron doping level and calcination temperature on hydrogen evolution reaction in acid medium of metal-free graphene aerogels

In this work, metal-free boron-doped graphene-based aerogels were successfully synthesized via a one-step autoclave assembly followed by freeze-drying and used as electrocatalysts for the hydrogen evolution reaction (HER) in acidic media. The synthesized reduced graphene oxide aerogels (rGOA) showed improved electrocatalytic activity by introducing boron and structural defects. The amount of boric acid used both as a dopant and reducing agent in the synthesis was optimized (boric acid/GO mass ratio = 17.5) to practically reach the crystallization limit of boric acid (boric acid/GO mass ratio = 20). It was observed that the higher the amount of boric acid added, the more boron was incorporated into the carbonaceous structure, improving the electrocatalytic activity of the final aerogel. Furthermore, calcination of the boron-doped electrocatalyst at 600 °C resulted in final aerogels with low oxygen content, moderate surface area, bimodal pore size distribution, and a high electrochemical active surface area. The final 3D graphene aerogel developed in this work, showed such outstanding electrocatalytic activity in HER as to replace noble metal-based electrocatalysts in the future.

Loading IrOx Clusters on MnO2 Boosts Acidic Water Oxidation via Metal-Support Interaction.

Noble metal-based electrocatalysts are crucial for efficient acidic water oxidation to develop green hydrogen energy. However, traditional noble metal catalysts loaded on inactive substrates show limited intrinsic catalytic activity, and their large sizes have compromised the atom efficiency of these noble metals. Herein, IrOx nanoclusters with sizes below 2 nm, displaying high atom-utilization efficiency of Ir species, were supported on a redox-active MnO2 nanosubstrate (IrOx/MnO2) with different phases (α-MnO2, δ-MnO2, and ε-MnO2) to explore the optimal combination. Electrochemical measurements showed that IrOx/ε-MnO2 had excellent OER performance with a low overpotential of 225 mV at 10 mA cm-2 in 0.5 M H2SO4, superior to its counterpart, IrOx/α-MnO2 (242 mV) and IrOx/δ-MnO2 (286 mV). Moreover, it also delivered robust stability with no obvious change in operating potential at 10 mA cm-2 during 50 h of continuous operation. Combining the XPS results and Bader charge analysis, we demonstrated that the strong metal-support interactions of IrOx/ε-MnO2 could effectively regulate the electronic structures of the active Ir atoms and stabilize IrOx nanoclusters on supports to suppress their detachment, resulting in significantly enhanced catalytic activity and stability for acidic OER. DFT calculations further supported that the enhanced catalytic OER performance of IrOx/ε-MnO2 could be ascribed to the appropriate strength of interactions between the active Ir sites and the reaction intermediates of the potential-determining step (*O and *OOH) regulated by the redox-active substrates.

Interface engineering of Ruddlesden–Popper perovskite/CeO2/carbon heterojunction for rechargeable zinc-air batteries

The development of noble metal-based bifunctional electrocatalysts is the key to driving the sluggish oxygen reduction/evolution reaction (ORR/OER) for rechargeable zinc-air battery applications. There is an urgent need to design and construct robust and cost-efficient bifunctional electrocatalysts. Herein, an interface engineering strategy of Ruddlesden–Popper (RP) perovskite/CeO2/carbon heterojunction with core–shell nanostructures is described. Ce-based metal–organic framework derived CeO2-C nanosheets are decorated on the surface of RP type perovskite Pr3Sr(Ni0.5Co0.5)3O10−δ (PSNC) nanofibers. Benefiting from the favorable conductivity, abundant oxygen vacancies and strong interfacial coupling, the hierarchical CeO2-C/PSNC electrode delivers a half-wave potential of 0.78 V (ORR), and an OER overpotential of 370 mV at 10 mA cm−2, respectively. A liquid rechargeable zinc-air battery (ZAB) assembled with CeO2-C/PSNC electrocatalysts as the air cathode exhibits a peak power density of 161 mW cm−2 and a long-term cycling life over 219 h. In addition, the CeO2-C/PSNC-based all-solid-state cable-type ZAB provides a high open-circuit voltage (∼1.44 V), good flexibility and durability. Our study opens a new insight into the design of efficient electrocatalysts for rechargeable ZABs by constructing hierarchical heterojunctions.

Far-from-equilibrium electrosynthesis ramifies high-entropy alloy for alkaline hydrogen evolution

High-entropy alloys (HEAs) provide an ideal platform for developing highly active electrocatalysts and investigating the synergy of mixed elements. Far-from-equilibrium synthesis holds great potential for fabricating HEAs at the nanoscale by rapidly shifting the thermodynamic conditions and manipulating the growth kinetics. While far-from-equilibrium synthesis of nanomaterials has been successful under thermochemical conditions, it is markedly challenging under electrochemical environments, as the use of an electrolyte limits the accessible temperature window and the temporal tunability of temperature. Herein, we demonstrate that applying a large electrochemical overpotential would create a far-from-equilibrium condition as changing the temperature of the system by considering the equation ΔG=ΔH−TΔS+nFΔψ. An electrochemical far-from-equilibrium approach is thus setup for constructing hierarchical and self-supporting high-entropy alloy nanostructures. The large overpotential drives the simultaneous reduction of multiple cations and the subsequent formation of a single-phase alloy. As a proof-of-concept, hierarchical Fe0.22Co0.18Ni0.18Cr0.14Cu0.28 was fabricated and used as an electrocatalyst for the hydrogen evolution reaction in alkaline media. The noble-metal-free HEA exhibits an overpotential of 84 mV at a current density of 10 mA cm–2, which is among the lowest even compared to noble metal-based electrocatalysts. This work opens a new avenue for building a variety of HEAs for energy and catalysis applications.

Construction and Prospect of Noble Metal‐Based Catalysts for Proton Exchange Membrane Water Electrolyzers

Engineering noble metal‐based electrocatalysts (NMEs) with high activity is of vital importance to accelerate the hydrogen production from proton exchange membrane water electrolyzers (PEMWEs). However, the poor stability and high price of NMEs greatly restrict the practical application. In this review, a series of strategies are summarized to boost the activity and reduce the cost of NMEs under acidic condition from the perspective of composition and structure optimization. The composition regulation through doping of metals or nonmetals can effectively inspire alloy effect or cocktail effect of NMEs, which provides an essential guidance to reduce the cost and enhance the stability of NMEs. Meanwhile, the structure optimization also directly improves the intrinsic activity of NMEs, which is comprehensively elaborated based on size, defect, and geometric effects. In addition, to extend the industrial application of PEMWEs, critical scientific issues behind the formulating of electrocatalyst slurry and coating method–PEMWEs performance relationships are fully clarified. Finally, the challenges for survivability of active center, catalytic mechanism research, and construction of membrane electrode are concluded. This review offers comprehensive and targeted guidelines for the rational design of NMEs for PEMWEs application.

Anodic electrodeposition of PbO2 on ATO/Ti with simultaneous doping of F, Co, and Fe as super-hydrophilic, highly active, and durable electrocatalyst for oxygen evolution reaction in acidic solution

The PbO2-based electrocatalysts were synthesized on antimony-doped tin oxide (ATO)/Ti substrate by anodic electrodeposition for oxygen evolution reaction (OER) in acidic media. Different additives, such as fluorine, iron, and cobalt ions, were used to modify the PbO2 performance for enhancement within the electrocatalytic stability and activity. The water contact angle (WCA) measurements showed that after activating the electrodes, the angles ranged from 8° to 12.5° (depending on the dopants type and amount). Fe and Co doping in the electrode led to a reduction of the anodic Tafel constant from 253 for PbO2-F to 198 and 207 mV.dec−1, respectively. Also, PbO2-F-Fe-Co exhibited the lowest overpotential at 10 mA.cm−2 (η10 = 0.307 V), which was incredibly reduced compared to the PbO2-F electrode (η10 = 0.637 V). An accelerated lifetime test (ALT) at an applied current density of 2.5 A.cm−2 reported an increase of 161 h (ca. four times) in the life of the F, Co, and Fe tri-doped lead dioxide compared to the undoped one. In addition, X-ray diffraction (XRD) along with microscopic, and electrochemical analyzes were performed after 10,000 voltammetric cycles to comprehend the deactivation mechanisms of the PbO2-F-Fe-Co electrode which was the most stable among all deposited electrodes. The results demonstrated that the PbO2-F-Fe-Co electrocatalyst can be a highly efficient and durable alternative to noble metal-based electrocatalysts in OER and provided valuable insights into effective and sustainable electrocatalysts.

Design and Synthesis of Noble Metal-Based Alloy Electrocatalysts and Their Application in Hydrogen Evolution Reaction.

Hydrogen energy is regarded as the ultimate energy source for future human society, and the preparation of hydrogen from water electrolysis is recognized as the most ideal way. One of the key factors to achieve large-scale hydrogen production by water splitting is the availability of highly active and stable electrocatalysts. Although non-precious metal electrocatalysts have made great strides in recent years, the best hydrogen evolution reaction (HER) electrocatalysts are still based on noble metals. Therefore, it is particularly important to improve the overall activity of the electrocatalysts while reducing the noble metals load. Alloying strategies can shoulder the burden of optimizing electrocatalysts cost and improving electrocatalysts performance. With this in mind, recent work on the application of noble metal-based alloy electrocatalysts in the field of hydrogen production from water electrolysis is summarized. In this review, first, the mechanism of HER is described; then, the current development of synthesis methods for alloy electrocatalysts is presented; finally, an example analysis of practical application studies on alloy electrocatalysts in hydrogen production is presented. In addition, at the end of this review, the prospects, opportunities, and challenges facing noble metal-based alloy electrocatalysts are tried to discuss.

Cu-doped Heterointerfaced Ru/RuSe2 nanosheets with optimized H and H2 O adsorption boost hydrogen evolution catalysis.

Ruthenium chalcogenide is a highly promising catalytic system as a Pt alternative for hydrogen evolution reaction (HER). However, well-studied ruthenium selenide (RuSe2 ) still exhibits sluggish HER kinetics in alkaline media due to the inappropriate adsorption strength of H and H2 O. Herein, w e report a new design of Cu-doped Ru/RuSe2 heterogeneous nanosheets (NSs) with optimized H and H2 O adsorption strength for highly efficient HER catalysis in alkaline media. Theoretical calculations reveal that the superior HER performance is attributed to a synergistic effect of the unique heterogeneous interface structure and Cu doping, which not only optimizes the electronic structure with a suitable d-band center to suppress proton overbinding but also alleviates the energy barrier with enhanced H2 O adsorption. As a result, Cu-doped heterogeneous Ru/RuSe2 NSs exhibit a small overpotential of 23mV at 10mA cm-2 , a low Tafel slope of 58.5mV dec-1 and a high turnover frequency (TOF) value of 0.88 s-1 at 100mV for HER in alkaline media, which is among the best catalysts in noble metal-based electrocatalysts toward HER. The present Cu-doped Ru/RuSe2 NSs interface catalyst is very stable for HER by showing no activity decay after 5000-cycle potential sweeps. This work heralds that heterogeneous interface modulation opens up a new strategy for the designing of more efficient electrocatalysts. This article is protected by copyright. All rights reserved.

Sphere-like Naphthalene-Based Microporous Nickel Phosphonate Facile for Asymmetric Supercapacitor Devices and Bifunctional Oxygen Electrocatalysts

To produce clean energy due to the lack of fossil fuels, the development of cost-effective and highly efficient energy storage devices and multifunctional electrocatalysts is essential to substitute noble metal-based electrocatalysts. In this context, transition metal-based nickel phosphonate material (NiNAP) has been synthesized using 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate and nickel nitrate hexahydrate in a hydrothermal reaction pathway in the absence of a templating pathway. The organic–inorganic hybrid structure with microporous arrays as a potential electrode material facilitates energy storage and conversion reactions. For the first time, a sphere-like NiNAP material has been developed, which is a potential electrode material for asymmetric supercapacitor applications with high specific capacitance and both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with a low overpotential and higher current density. Moreover, the NiNAP material exhibits a specific capacitance of 4456 F g–1 in three-electrode assembly and 455 F g–1 in asymmetric supercapacitor at a scan rate of 1 mV s–1, where the energy and power density are estimated to be 204 W h kg–1 and 409 W kg–1, respectively. Interestingly, the NiNAP material displays outstanding catalytic activity toward OER with a low overpotential of 242 mV at the current density of 10 mA cm–2 and excellent ORR activity with an onset potential of 0.74 V vs RHE. Also, it shows long-term stability without significant changes in the current density for OER and ORR.