Bifunctional Electrocatalytic Activity Research Articles

Boosting the bifunctional electrocatalytic activity of nitrogen-doped graphene by electronic effect of heterovalent ion substituted perovskite oxides

Sluggish reaction kinetics of carbon-based catalysts hinder their activity in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which further impede commercialization of Zinc-air batteries. Here, a strategy of modifying the electronic structure of nitrogen-doped graphene (NG) through constructing it with cobalt (Co) substituted manganese-based perovskite oxides (LaMn1-xCoxO3) to accelerate its activity in OER and ORR is proposed. Co substitution is beneficial for donating electrons to oxygen-containing intermediates by inducing excessive negative charge on NG to improve kinetics in OER and ORR. The half-wave potential in ORR for LaMn0·6Co0·4O3@NG is 0.74 V, higher than that of LaMnO3@NG and LaCoO3@NG; the overpotential of LaMn0·6Co0·4O3@NG at 10 mA cm−2 is 314 mV for OER, smaller than that of LaMnO3@NG and LaCoO3@NG, supposing the superior electrochemical activity of composite catalyst with Co substitution in OER and ORR. This research offers a way in fabricating high efficient and cost-effective bifunctional electrocatalyst for Zinc-air batteries.

Zinc-Substituted Cobalt Phosphate [ZnCo2(PO4)2] as a Bifunctional Electrocatalyst.

Development of highly efficient, earth-abundant, and stable bifunctional electrocatalysts is pivotal for designing viable next-generation metal-air batteries. Cobalt-based phosphates provide a treasure house to design electrocatalysts, with a wide range of cation substitutions to further enhance their electrocatalytic activity. In particular, phosphates with distorted geometry show favorable binding efficiency toward water molecules with low overpotential. In the present work, zinc-substituted cobalt phosphate ZnCo2(PO4)2 was investigated. Its crystal structure was solved to a monoclinic framework built with CoO6 octahedra and distorted CoO5/ZnO5 trigonal bipyramid leading to efficient bifunctional electrocatalytic activity. It offers robust structural stability with onset potential values of 0.87 V (vs reversible hydrogen electrode (RHE)) and 1.50 V (vs RHE) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes, respectively, comparable to the precious metal catalysts. The origin and stability of the bifunctional activity were probed by combining ex situ diffraction and electron microscopy corroborated by ab initio calculations. Overall, zinc-substituted cobalt phosphate [ZnCo2(PO4)2] forms a potential bifunctional electrocatalyst with tunable local cobalt coordination that can be harnessed for metal-air batteries.

Tailoring the d-band electronic structure of deficient LaMn0.3Co0.7O3-δ perovskite nanofibers for boosting oxygen electrocatalysis in Zn-Air batteries

The development and design of efficient bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for rechargeable Zinc-air batteries (ZABs). Optimizing the d-band structure of active metal center in perovskite oxides is an effective method to enhance ORR/OER activity by accelerating the rate-determining step. Herein, we report a deficient method to optimize the d-band structure of Co ions in LaMn0.3Co0.7O3-δ (LMCO-2) perovskite nanofibers, which regulates the mutual effect between B-site Co ions and reactive oxygen intermediates. It is proved by experiment and theoretical calculation that the d-band center (Md) of transition metal ions in LMCO-2 is moved up and the electron filling number of eg orbital in B site is 1.01, thus leading to the reduction of Gibbs free energy required for ORR rate-determining step (OH*→H2O*) to 0.22 eV and promoting reaction proceeds. In this manner, LMCO-2 showed good bifunctional oxygen electrocatalytic activity, with a half-wave potential of 0.71 V vs. RHE. Furthermore, the high specific capacity of 811.54 mAh g−1 and power density of 326.56 mW cm−2 were obtained by using LMCO-2 as the cathode catalyst for ZABs. This study proved the feasibility of d-band structure regulation to enhance the electrocatalytic activity of perovskite oxides.

Heterogeneous bimetallic oxysulfide nanostructure (Ni-Co) as hybrid bifunctional electrocatalyst for sustainable overall alkaline simulated seawater splitting

The design and development of high performance non-precious bifunctional electrocatalytic activity for oxygen/hydrogen evolution reaction (OER/HER) remains a significant challenge in overall seawater splitting process. Herein, we report the Co3S4/Co3O4 hybrid nanostructures catalyst with duel functions is successfully in-situ synthesized through self-templating strategy, whereas, Ninanostructure 3S2/NiO are grown on Ni foam using a facile hydrothermal reaction and post thermal annealing process. The designed self-standing Co3O4(Co3S4)/NiO(Ni3S2)/NF nanostructure (denoted as Co-Ni-S/NF) as a self-standing hybrid electrode demonstrates an excellent bifunctional electrocatalytic activity for OER and HER process in alkaline freshwater/alkaline simulated seawater as electrolyte. Taking advantage of the bimetallic synergistic effect and formation of an efficient interface layer of Ni3S2/NiO in a unique nanostructure, the resultant bifunctional electrocatalytic performance of Co-Ni-S/NF electrode for OER & HER processes are highly performed in both electrolyte conditions. Specifically, Co-Ni-S/NF hybrid electrode requires lower overpotentials of 270 mV (at 20 mV cm−2), 310 mV (at 50 mV cm−2) for OER and lower overpotentials of 239 mV (at 20 mV cm−2), 291 mV (at 50 mV cm−2) for HER in alkaline simulated seawater condition. For two-electrode based electrolyzer analyses, Co-Ni-S/NF electrode based electrolyzer demonstrates low cell voltage of 1.67 V to attain a current density of 10 mA cm−2 with stable activity of overall alkaline simulated seawater splitting process whereas hybrid electrode used as anode and cathode. Therefore, the proposed interface engineering strategy and rationally constructing electrocatalyst nanostructure via a self-templating route could be a promising opportunity to develop an active duel functional catalyst for direct seawater splitting applications.

Ce‐Induced Differentiated Regulation of Co Sites via Gradient Orbital Coupling for Bifunctional Water‐Splitting Reactions

AbstractRare‐earth (RE) elements have emerged as crucial promoters to regulate the electrocatalysis of transition metals (TM), but knowledge about the RE‐enhanced mechanism of TM in electrocatalysis is limited. Herein, an array‐like Ce‐CoP catalyst is constructed to explore the origin and distinction of the Ce‐induced enhanced mechanism of Co sites in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Compared with individual CoP, the developed Ce‐CoP exhibits superior bifunctional electrocatalytic activity with the overpotentials of 81 and 240 mV at 10 mA cm−2, respectively for HER and OER, with excellent electrocatalytic stability. Theoretical calculations show that the unique 4f valence electron structure of Ce endows the Co sites with differentiated regulation in the HER and OER through f‐p‐d gradient orbital coupling. In the HER, the retained Ce‐4f state induces electron spin parallelism at the surrounding Co sites, promoting the adsorption of *H intermediates. While in the OER, the Ce‐4f band acts as sacrificing band to protect the Co sites from overoxidation through the Ce‐O‐Co chain with an optimized Co‐3d state, providing additional spin coupling with oxygen intermediates. These findings provide new insights into comprehending the RE‐enhanced mechanism of electrocatalysis and present valuable design guidelines for the development of efficient multi‐functional electrocatalysts.

In situ grown three-dimensional porous Co3O4/graphdiyne oxide hybrid nanomaterials with sea urchin-like structures for high-performance zinc–air batteries

As a promising energy conversion system, zinc air battery (ZAB) usually suffers from short cycle life and poor reversibility due to the slow kinetics of the redox reaction on the air cathode, making it a big-barriers in practical applications. Herein, three-dimensional (3D) porous Co3O4/graphdiyne oxide (GDYO) hybrid nanomaterials with sea urchin-like structures have been prepared by in-situ epitaxial growth. The 3D porous Co3O4/GDYO hybrid nanomaterials with sea urchin-like structures expand the larger contact area between the electrolyte and the electrode, which provide abundant channels for ion diffusion and electron transport with enhanced charge transfer kinetics and structural stability. The 3D porous Co3O4/GDYO hybrid nanomaterials with sea urchin-like structures shows excellent bifunctional electrocatalytic activity for both oxygen evolution reaction (OER) (onset potential of 1.38 V, overpotential of 335 mV at 10 mA cm−2) and oxygen reduction reaction (ORR) (onset potential of 0.84 V, half-wave potential of 0.6 V). ZABs fabricated with 3D porous Co3O4/GDYO hybrid nanomaterials as cathode display a high power density of 96 m W cm−2, an open circuit voltage of 1.53 V, as well as a specific capacity of 799.5 mA h g−1 (at 10 mA cm−2) and a corresponding energy density of 965 Wh kg−1. Further, its charge and discharge voltages remain stable for over 400 h at a constant current charge–discharge cycling of 3 mA cm−2. This work offers novel insights on developing excellent bifunctional electrocatalysts for both OER and ORR, which expands a new application of GDYO on ZABs.

Ba-doped LaCoO3 perovskite as novel bifunctional electrocatalyst for zinc–air batteries

Developing efficient non-noble metal bifunctional cathode catalysts to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a major challenge for zinc–air batteries (ZABs). In the present study, a series of La1−xBaxCoO3 (x = 0, 0.05, 0.10, 0.15, 0.20) perovskite-type oxides were prepared via self-propagating high-temperature synthesis and evaluated as the bifunctional electrocatalytic activity for ZABs. Among the samples, La0.85Ba0.15CoO3 showed the best bifunctional catalytic activity, in which the Eonset of ORR at 0.1 mA cm−2 and the Ej of OER at 10 mA cm−2 in 0.1 M KOH solution were 0.829 and 1.685 V vs.RHE, respectively. Besides, the La0.85Ba0.15CoO3 catalyst was evaluated as an air electrode for ZABs, displaying a high power density of 116.2 mW cm−2 at the current density of 233.8 mA cm−2 and a stable charge–discharge voltage gap of 0.98 V after 1200 cycles, with superior cycling stability over 200 h. Characterization analysis revealed that the enhancement of bifunctional electrocatalytic activity was attributed to the larger specific surface area and increase in oxygen vacancy. Thus, the Ba-doped LaCoO3 material is a promising bifunctional electrocatalyst for ZABs.

Active sites engineering construction of spinel cobalt oxide based excellent bifunctional electrocatalyst for water splitting by modifying oxygen vacancy with S dopant

It is a significant and challenging work to endow transition metal oxide highly bifunctional electrocatalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, the bifunctional electrocatalysts of S-doped FeCo2O4 ultrafine nanoparticles were fabricated by introducing rich oxygen vacancies (Vo) and then partially substituting the Vo by doping S atoms. The electronic structures and adsorption free energy of the active sites towards reactants were modulated by the strategy of doping sulfur atoms to modify oxygen vacancies. The catalysts were consequently endowed extraordinarily improved HER and OER electrocatalytic activities. The optimized catalyst S-doping FeCo2O4 (FCOS-10) exhibited 33 and 59 times of the turnover frequency as high as that of the pristine FeCo2O4 for HER and OER, respectively. Only 1.54 V of cell voltage for water electrolysis is needed to afford 10 mA cm−2. The catalyst also exhibited robust stability of 85.4% after 120 h i-t test for overall water splitting and high Faraday efficiency of 97.19%, thus it is a high promising catalyst for commercial water electrolysis. This work is one of the few examples that endow metal oxide with highly bifunctional activities for HER and OER, and it is an important reference for rational designing and fabrication of analogous catalysts.

NiCoP nanoparticles embedded in coal-based carbon nanofibers as self-supporting bifunctional electrocatalyst toward water splitting

The high activity and prolonged stability of bifunctional electrocatalysts are significant prerequisites for electrocatalytic water splitting. Recently, it has been proven that the performance of electrocatalysts can be elevated by optimizing components and constructing self-supporting electrodes. Herein, the well-proportioned NiCoP nanoparticles embedded in self-supporting coal-based carbon nanofibers (NiCoP@C-CNFs-2) are fabricated by electrospinning and pyrolysis process with the help of phytic acid and oxidized coal. The phytic acid not only chelates Ni and Co ions to disperse the active sites but serves as a green phosphorus source to prepare the well-proportioned NiCoP nanoparticles. Meanwhile, benefiting from coal-based carbon nanofibers with high electrical conductivity and excellent mechanical strength, the obtained self-supporting NiCoP@C-CNFs-2 is endowed with good bifunctional electrocatalytic activity and stability. The NiCoP@C-CNFs-2 severally provides overpotentials of 121 and 259 mV for HER and OER at 10 mA cm−2 in 1.0 M KOH electrolyte. Furthermore, an alkaline electrolyzer with NiCoP@C-CNFs-2 as bifunctional electrocatalysts requires 1.636 V voltage and maintains superior stability over 50 h at 10 mA cm−2. This work opens a reasonable avenue to design simple and efficient self-supporting carbon nanofibers electrocatalysts.

Tailoring Metal-Organic Frameworks and Derived Materials for High-Performance Zinc-Air and Alkaline Batteries.

Developing multifunctional materials from earth-abundant elements is urgently needed to satisfy the demand for sustainable energy. Herein, we demonstrate a facile approach for the preparation of a metal-organic framework (MOF)-derived Fe2O3/C, composited with N-doped reduced graphene oxide (MO-rGO). MO-rGO exhibits excellent bifunctional electrocatalytic activities toward the oxygen evolution reaction (ηj=10 = 273 mV) and the oxygen reduction reaction (half-wave potential = 0.77 V vs reversible hydrogen electrode) with a low ΔEOER-ORR of 0.88 V in alkaline solutions. A Zn-air battery based on the MO-rGO cathode displays a high specific energy of over 903 W h kgZn-1 (∼290 mW h cm-2), an excellent power density of 148 mW cm-2, and an open-circuit voltage of 1.430 V, outperforming the benchmark Pt/C + RuO2 catalyst. We also hydrothermally synthesized a Ni-MOF that was partially transformed into a Ni-Co-layered double hydroxide (MOF-LDH). A MO-rGO||MOF-LDH alkaline battery exhibits a specific energy of 42.6 W h kgtotalmass-1 (106.5 μW h cm-2) and an outstanding specific power of 9.8 kW kgtotalmass-1 (24.5 mW cm-2). This work demonstrates the potential of MOFs and MOF-derived compounds for designing innovative multifunctional materials for catalysis, electrochemical energy storage, and beyond.

Phosphate-decorated Fe-N-C to promote electrocatalytic oxygen reaction activities for highly stable zinc-air batteries

An obvious challenge for rechargeable Zn-air batteries (ZABs) is the impact of large charge potentials on the oxidation of their cathode catalysts, which accelerates the corrosion of the carbon electrodes, and significantly compromises their stability. It is therefore necessary to design simple methods aimed at facilitating the oxygen evolution reaction (OER) processes of ZABs to suppress the corrosion of their cathode materials. Herein, a biomass-derived N-doped porous carbon material coupled with Fe3O4 and Fe2N nanoparticles and modified with phosphorus (P-Fe3O4/Fe2N@NPC) was designed as an air-cathode to reduce the charging voltage of ZABs. It exhibited excellent ORR/OER bifunctional electrocatalytic activities, and the assembled ZAB displayed an ultra-long service life. DFT calculations showed that the P-modification modulated the electronic state and coordination environment of the active iron atom, thereby significantly enhancing the OER activity of P-Fe3O4/Fe2N@NPC.

Theoretical Investigation of HER and OER Electrocatalysts Based on the 2D R-graphyne Completely Composed of Anti-Aromatic Carbon Rings.

Based on the DFT calculations, two-dimensional (2D) R-graphyne has been demonstrated to have high stability and good conductivity, which can be conducive to the relevant electrocatalytic activity of the material. Different from the poor graphene, R-graphyne, which is completely composed of anti-aromatic structural units, can exhibit certain HER catalytic activity. In addition, doping the TM atoms in Group VIIIB can be considered an effective strategy to enhance the HER catalytic activity of R-graphyne. Particularly, Fe@R-graphyne, Os@R-graphyne, Rh@R-graphyne and Ir@R-graphyne can exhibit higher HER catalytic activities due to the formation of more active sites. Usually, the shorter the distance between the TM and C atoms is, the better the HER activity of the C-site is. Furthermore, doping Ni and Rh atoms of Group VIIIB can significantly improve the OER catalytic performance of R-graphyne. It can be found that ΔGO* can be used as a good descriptor for the OER activities of TM@R-graphyne systems. Both Rh@R-graphyne and Ni@R-graphyne systems can exhibit bifunctional electrocatalytic activities for HER/OER. In addition, all the relevant catalytic mechanisms are analyzed in detail. This work not only provides nonprecious and highly efficient HER/OER electrocatalysts, but also provides new ideas for the design of carbon-based electrocatalysts.

Geometric and Electronic Engineering of Atomically Dispersed Copper-Cobalt Diatomic Sites for Synergistic Promotion of Bifunctional Oxygen Electrocatalysis in Zinc-Air Batteries.

The development of rechargeable zinc-air batteries is heavily dependent on bifunctional oxygen electrocatalysts to offer exceptional oxygen reduction/evolution reaction (ORR/OER) activities. However, the design of such electrocatalysts with high activity and durability is challenging. Herein, a strategy is proposed to create an electrocatalyst comprised of copper-cobalt diatomic sites on a highly porous nitrogen-doped carbon matrix (Cu-Co/NC) with abundantly accessible metal sites and optimal geometric and electronic structures. Experimental findings and theoretical calculations demonstrate that the synergistic effect of Cu-Co dual-metal sites with metal-N4 coordination induce asymmetric charge distributions with moderate adsorption/desorption behavior with oxygen intermediates. This electrocatalyst exhibits extraordinary bifunctional oxygen electrocatalytic activities in alkaline media, with a half-wave potential of 0.92 V for ORR and a low overpotential of 335mV at 10mAcm-2 for OER. In addition, it demonstrates exceptional ORR activity in acidic (0.85V) and neutral (0.74V) media. When applied to a zinc-air battery, it achieves extraordinary operational performance and outstanding durability (510h), ranking it as one of the most efficient bifunctional electrocatalysts reported to date. This work demonstrates the importance of geometric and electronic engineering of isolated dual-metal sites for boosting bifunctional electrocatalytic activity in electrochemical energy devices.

Fascinating Bifunctional Electrocatalytic Activity via a Mesoporous Structured FeMnO3@ZrO2 Matrix as an Efficient Cathode for Li–O2 Batteries

Nonaqueous Li–O2 batteries have remarkable potential for use in future-generation sustainable green energy storage systems. Perovskites of the type ABO3 provide bifunctional electrocatalytic activity superior to that of dual mixed-metal oxides due to the presence of crystallographic defects and oxygen vacancies, arising from the multivalency of the A and B cations. In this study, we used a facile hydrothermal method with an ammonia solution to modify coralline-like ZrO2 with Fe0.5Mn0.5O3 (FeMnO3) and graphene nanosheets (GNSs). The porous structure of the resulting ZrO2@FeMnO3/GNS system featured a high surface area and large volume, thereby exposing a great number of active sites. X-ray photoelectron spectroscopy revealed that the surface of the as-synthesized FeMnO3@ZrO2/GNS cathode material was rich with oxygen vacancies (i.e., a huge quantity of defects). This coralline-like bifunctional electrocatalyst possessed effective redox capability between Li2O2 and O2 as a result of its excellent catalytic activity in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). We examined the charge/discharge behavior of corresponding electrodes (EL-cell type for Li–O2 battery) in the voltage range of 2.0–4.5 V (vs Li/Li+). The synergistic effects of the high catalytic ability and coralline-like microstructure of our ZrO2@FeMnO3/GNS catalyst for Li–O2 batteries resulted in its superior rate capability and excellent long-term cyclability, sustaining 100 cycles at 100 mA g–1 with a limited capacity of 1000 mAh g–1. The cell overpotential was ∼0.14 V when adding LiI as a redox mediator, resulting in a more practical Li–O2 battery with the ZrO2@FeMnO3/GNS catalyst. Therefore, ZrO2@FeMnO3/GNS catalysts having distinctive coralline-like structures can display outstanding bifunctional catalytic activity and electrical conductivity, suggesting great potential for enhanced Li–O2 battery applications.

Nitrogen-Rich Porous Carbon Nanotubes Coated Co/Mo2N Composites Derived from Metal-Organic Framework as Efficient Bifunctional Oxygen Electrocatalysts

Noble metal catalysts such as Pt/C and RuO2 are the most efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts and show excellent activity. However, their high costs, scarcity, single function, and weak durability impede their large-scale practical application. Therefore, it is paramount to design bifunctional electrocatalysts with high activity, long durability, and low cost. In this work, we used the functionalized modification and hierarchical porous structure of MOFs and adjusted the ratio of Co/Mo atoms to prepare uniformly dispersed nanospheres. The uniform porous nitrogen-doped carbon nanotubes coated with Co/Mo2N composites were obtained by trapping the volatile CNx during high-temperature pyrolysis via a vapor deposition strategy. The physical and chemical properties of the materials were analyzed by various characterization methods such as XRD, XPS, TEM, SEM, Raman, and BET. Notably, CoMoN@NCNTs-700 exhibited excellent ORR/OER bifunctional electrocatalytic activity in alkaline conditions due to the synergistic effect of porous nitrogen-doped carbon nanotubes and the unique heterostructure of Co/Mo2N. In 0.1 M KOH, its ORR half-wave potential was E1/2 = 0.78 V, with a limiting current density even reached to 5.3 mA cm−2 and its operating potential was 1.60 V at a current density of 10 mA cm−2. At the same time, CoMoN@NCNTs-700 also showed better stability and methanol resistance than the commercial catalysts. This work provides a valuable reference for the design and construction of inexpensive non-noble metal bifunctional electrocatalysts.

A Stable Imide‐Linked Metalphthalocyanine Framework with Atomically Dispersed Fe‐N4 Sites and Ultrafine Nickel Oxide Nanoparticles to Boost Reversible Oxygen Electrocatalysis with a Record‐Low ΔE of 0.59 V

AbstractMetallophthalocyanines (MPcs) hold great promise in the electrochemical reduction of oxygen; however, their practical applications in energy storage and conversion are still limited by their low stability and poor water oxidation activity. Herein, a novel stable 2D imide‐linked metalphthalocyanine framework (denoted as FePc‐PI) is reported, that has atomically dispersed Fe‐N4 sites deposited on the KB substrate via in situ growth, followed by incorporation of ultrafine nickel oxide nanoparticles (NiOx@FePc‐PI/KB) to induce bifunctional electrocatalytic activities for the oxygen reduction reaction and oxygen evolution reaction. Benefitting from the robust aromatic backbone, the engineered catalytic centers, and the unique electronic structures owing to the interaction between the Fe‐N4 sites and NiOx species, the newly developed NiOx@FePc‐PI/KB catalyst exhibits excellent reversible oxygen bifunctional activity (E1/2 = 0.926 V, η10 = 285 mV), delivering a record‐low overpotential difference (ΔE) of 0.59 V, which far exceeds the noble‐metal‐based Pt/C+RuO2 benchmark (ΔE = 0.77 V) and represents the highest level for reported bifunctional electrocatalysts. Furthermore, the rechargeable aqueous Zn‐air batteries assembled with the NiOx@FePc‐PI/KB catalyst deliver a high peak power density of 232.9 mW cm−2 and long‐term cycling durability over 1400 cycles. Flexible all‐solid‐state Zn‐air batteries exhibit stable cycling at various flat/bent/flat states, thus demonstrating their excellent prospects in realistic implementations.

3D Porous N and S Co-doped CNT Microspheres with Highly Dispersed CoP Nanoparticles: Toward an Efficient Bifunctional Electrocatalyst for Zn-Air Batteries

The design and efficient synthesis of oxygen redox electrocatalysts possessed with high activity are of the essence for advanced rechargeable Zn-air batteries (ZABs). In particular, porous architectures composed of transition metal compound and carbonaceous material have attracted significant attention owing to their enhanced electrocatalytic activity. This study reports the fabrication of metal-free N and S co-doped porous CNT microspheres (3DNSCNT) via spray drying and subsequent post-treatment. Moreover, to hybridize with metal phosphide, CoP nanoparticles are uniformly decorated on the microspheres (3DNSCNT/CoP) by the hydrothermal method and phosphidation treatment. Due to the effect of the combination of the porous architecture inside the entangled 3DNSCNT and uniformly deposited CoP nanoparticles, 3DNSCNT/CoP exhibits superior bifunctional electrocatalytic activities for oxygen redox reaction in 0.1 M KOH electrolyte compared with noble metal-based catalysts like Pt and Ru. Furthermore, as an air cathode for ZABs, 3DNSCNT/CoP exhibits a high-power density (177 mW cm-2), low polarization overpotential, and durable cycle performance (200 h).

Quick-to-synthesize hybrid electrodes composed of activated carbon cloth with Co/Fe-based films as bifunctional electrocatalysts for water splitting

Hybrid electrodes have recently been investigated as attractive alternatives to noble-metal-based electrocatalysts for hydrogen production by water splitting. Herein, we propose an electrode composed of an oxidized carbon cloth with an electrodeposited bimetallic Co/Fe-based film. By optimizing the electrodeposition conditions and applying electrochemically activated carbon cloth as a substrate, one can prepare a free-standing noble-metal-free electrocatalytic electrode with high bifunctional electrocatalytic activity in hydrogen and oxygen evolution from alkaline solution. The developed Fe0.25Co0.75 electrode requires overpotentials of 245 mV for HER and 360 mV for OER at high current densities of −100 and 100 mA cm−2, respectively. Furthermore, its overall synthesis time from commercially available raw materials is only approximately 20 min. The electrode material was used as both a cathode and an anode in the model electrolyzer, which can deliver 10 mA cm−2 of current density at 1.66 V without loss of activity during 100 h of performance.

The underlying mechanism trade-off between particle proximity effect and low-Pt loading for oxygen reduction and methanol oxidation reaction activity

Highly efficient and stable Pt-based electrocatalysts have broad application prospects in fuel cells, among which, Pt loading accompanied with particle size, interparticle distance (ipd), and interaction with support are identified as key contributors for high activity and selectivity. Herein, we have developed the nitrogen-doped graphite-like carbon sheets supporting low-Pt loading (Pt@N-GC) with uniform size and controllable ipd, and disentangled the main effect of ipd on oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activity. The optimal 5.0 wt% low-Pt loading results in more abundant Pt sites and lower ipd, which leads to the higher surface reactivity by proximity effect, and 2e− pathway can be hindered by strongly resorbing and reducing H2O2 to promote 4e− pathway towards ORR. Simultaneously, the 5.0 wt% Pt@N-GC can effectively improve the MOR activity, enhance the adsorption of -OH group under the appropriate ipd, so as to promote the instantaneous oxidation of CO and enhance the tolerance, and accelerate the oxidative dehydrogenation of methanol. Benefiting by the synergistic effect of Pt nanoparticles and N-GC support, all Pt@N-GCs exhibit bifunctional electrocatalytic activity and durability. We believe the gained trade-off of the loading and proximity effect of Pt, and its influence on catalytic activity and selectivity contributes to design more promising low-Pt loading bifunctional catalysts for fuel cell.

Perovskite oxide composites for bifunctional oxygen electrocatalytic activity and zinc-air battery application- a mini-review

Zinc-air batteries (ZABs) are considered as a potential alternative to next-generation batteries. However, the slow reaction kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), involved in the charging and discharging of ZAB hinder their real-world applicability. Thus, developing an excellent bifunctional OER/ORR electrocatalyst that exhibits solid cyclic stability is crucial. Perovskite oxides are known for their composition and structural flexibility, which allows for the modulation of the electronic structure of electrocatalysts by incorporating foreign metals into oxides, resulting in improved oxygen electrocatalytic activity. Achieving bifunctional oxygen electrocatalytic activity through a single pristine perovskite oxide is challenging due to the requirement of different reaction steps. Building heterostructures by combing perovskite oxides with metal, metal alloys, metal hydroxides, metal oxides, spinel oxides, and N-doped carbon materials enhances the active sites of the catalyst for bifunctional activity and ZAB application. In this review, we discuss the mechanism involved in ZAB and bifunctional oxygen electrocatalytic activity, mainly focusing on perovskite oxide heterostructure synthesizing strategies and their performance in ZAB. This review aims to pave the way for designing inexpensive perovskite oxide-based electrocatalysts and tailoring the active sites for improved energy conversion and industrialization.