Non-precious Metal Bifunctional Electrocatalysts Research Articles

Optimizing the Ratio of Metallic and Single-Atom Co in CoNC via Annealing Temperature Modulation for Enhanced Bifunctional Oxygen Evolution Reaction/Oxygen Reduction Reaction Activity

Developing low-cost, efficient alternatives to catalysts for bifunctional oxygen electrode catalysis in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for advancing the practical applications of alkaline fuel cells. In this study, Co particles and single atoms co-loaded on nitrogen-doped carbon (CoNC) were synthesized via pyrolysis of a C3N4 and cobalt nitrate mixture at varying temperatures (900, 950, and 1000 °C). The pyrolysis temperature and precursor ratios were found to significantly influence the ORR/OER performance of the resulting catalysts. The optimized CoNC-950 catalyst demonstrated exceptional ORR (E1/2 = 0.85 V) and OER (Ej10 = 320 mV) activities, surpassing commercial Pt/C + RuO2-based devices when used in a rechargeable zinc–air battery. This work presents an effective strategy for designing high-performance non-precious metal bifunctional electrocatalysts for alkaline environments.

Sn doped cobalt-based phosphide as bifunctional catalyst for ethanol oxidation reaction and hydrogen evolution reaction

The development of non-precious metal bifunctional electrocatalysts is of practical significance to solve resource shortage and energy crisis. In this study, to accelerate mass/electron transfer and maximize the area of exposed active sites, a coral-like Sn–Co–P/NF bi-functional electrocatalyst was synthesized by electrodeposition for total hydrolysis. Ethanol oxidation reaction (EOR) was used to replace oxygen evolution reaction (OER) with hydrogen evolution reaction (HER) to further improve the water electrolysis rate. The catalyst showed great electrochemical activity and stability in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions. At a current density of 10 mA cm−2, the required overpotential for HER is only 59 mV (vs. RHE) and 304 mV (vs. RHE) for OER, and the corresponding Tafel slopes are 42 mV·dec−1 and 67 mV·dec−1, respectively. When EOR was substituted for anodic oxygen evolution, the overpotential could be reduced by 240 mV. In addition, when Sn–Co–P/NF is used as a water-ethanol electrolytic cell assembled with anode and cathode, the current density of 10 mA cm−2 can be reached with only 1.49 V operating voltage, which is 130 mV lower than that of hydrolysis alone, and it also shows good durability in the test of 28 h. Therefore, the experimental results show that it is feasible to use EOR instead of OER to coupling with HER, the catalyst has broad application prospects in industrial electrolysis.

Novel and superhydrophilic bifunctional NiCuMn@TiN nanosheets supported on iron foam for high-performance supercapacitors and water oxidation

Synthesizing low-cost and highly efficient bifunctional electrocatalysts for hybrid supercapacitors and oxygen evolution reaction (OER) is critically essential for the progress of energy storage and conversion devices. Therefore, a novel, inexpensive and superhydrophilic bifunctional NiCuMn@TiN nanosheet supported on iron foam (NiCuMn@TiN/IF) is successfully designed and fabricated via spent cupronickel (SCN) as Ni and Cu precursor by a facile one-step electrosynthesis routine. With adding nano titanium nitride (TiN), the obtained NiCuMn@TiN/IF composite electrode not only possesses a large superhydrophilic surface that enhances ion/electron transfer efficiency and provides numerous activity sites for the electrochemical reaction but also achieves efficient recovery of metal resources using the secondary resource SCN as soluble anode further reduces the cost of electrode preparation. And since the synergistic effect of large specific surface area and superhydrophilicity, the NiCuMn@TiN/IF delivers a high specific capacity of 22.5 F cm−2 at 10 mA cm−2 in 3 M KOH and also illustrates superior OER activity with an extremely low overpotential (286 mV) and remarkable durability at a high current density of 100 mA cm−2 in 1 M KOH. This research provides a solid foundation for the large-scale preparation of low-cost and high-performance non-precious metal bifunctional electrocatalysts for the commercial development of electrochemical supercapacitors and electrochemical water-to-hydrogen conversion technology.

Facile construction Co-doped and CeO2 heterostructure modified NiS2 grown on foamed nickel for high-performance bifunctional water electrolysis catalysts

The development of cost-effective non-precious metal bifunctional electrocatalysts with performance comparable to that of precious metal-based catalysts is an important factor in achieving industrial hydrogen production from electrolytic water. In order to prepare electrocatalysts with highly exposed active sites and high intrinsic activity, unique heterostructure and element doped 2D Co–NiS2/CeO2 nanosheets grown on foamed nickel (Co–NiS2/CeO2/NF) are prepared by hydrothermal reaction and annealing. The Co–NiS2/CeO2/NF catalyst demonstrates excellent performance and stability in alkaline solutions. In 1.0 M KOH solution, the overpotentials for the HER and OER were found to be as low as 88 mV and 240 mV, respectively. Moreover, when utilized as both the anode and cathode in a standard two-electrode water electrolyzer, Co–NiS2/CeO2/NF delivers 50 mA cm−2 at a relatively low voltage of 1.82 V and was able to maintain its high performance levels without any degradation even after 48 h of CP test. The combination of doping and interfacial effects greatly increases the number of active sites and the activity of the catalyst. This study provides a new pathway for the design of cost-effective, high-performance catalytic materials for overall water splitting.

Interfacial Engineering of Leaf-like Bimetallic MOF-Based Co@NC Nanoarrays Coupled with Ultrathin CoFe-LDH Nanosheets for Rechargeable and Flexible Zn-Air Batteries.

Exploring high-efficiency, low-cost, and long-life bifunctional self-supporting electrocatalysts is of great significance for the practical application of advanced rechargeable Zn-air batteries (ZABs), especially flexible solid-state ZABs. Herein, ultrathin CoFe-layered double hydroxide (CoFe-LDH) nanosheets are strongly coupled on the surface of leaf-like bimetallic metal-organic frameworks (MOFs)-derived hybrid carbon (Co@NC) nanoflake nanoarrays supported by carbon cloth (CC) via a facile and scalable method for rechargeable and flexible ZABs. This interfacial engineering for CoFe-LDHs on Co@NC improves the electronic conductivity of CoFe-LDH nanosheets as well as achieves the balance of oxygen evolution reduction (OER) and oxygen reduction reaction (ORR) activity. The unique three-dimensional (3D) open interconnected hierarchical structure facilitates the transport of substances during the electrochemical process while ensuring adequate exposure of OER/ORR active centers. When applied as an additive-free air cathode in rechargeable liquid ZABs, CC/Co@NC/CoFe-LDH-700 demonstrates high open-circuit potential of 1.47 V, maximum power density of 129.3 mW cm-2, and satisfactory specific capacity of 710.7 mAh g-1Zn. Further, the flexible all-solid-state ZAB assembled by CC/Co@NC/CoFe-LDH-700 displays gratifying mechanical flexibility and stable cycling performance over 40 h. More significantly, the series-connected flexible ZAB is further verified as a chain power supply for LED strips and performs well throughout the bending process, showing great application prospects in portable and wearable electronics. This work sheds new light on the design of high-performance self-supporting non-precious metal bifunctional electrocatalysts for OER/ORR and air cathodes for rechargeable ZABs.

Ultralow ruthenium modification of cobalt metal-organic frameworks for enhanced efficient bifunctional water splitting.

Hydrogen economy has emerged as a promising alternative to the current hydrocarbon economy. It involves harvesting renewable energy to split water into hydrogen and oxygen and then further utilising clean hydrogen fuel for various applications. The rational exploration of advanced non-precious metal bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for efficient water splitting. Herein, an ultralow Ru-modified cobalt metal-organic framework (CoRu0.06-MOF/NF) two-dimensional nanosheet array bifunctional catalyst was fabricated through a strategy under mild experimental conditions. The obtained CoRu0.06-MOF/NF exhibited excellent bifunctional electrocatalytic activity and stability in alkaline media, with low overpotentials of 37 and 181 mV and significant durability for more than 95 and 110 h toward the HER and OER at 10 mA cm-2, respectively. The experimental results showed that the two-dimensional nanoarray structure had a large specific surface area and abundant exposed active sites. Additionally, ultralow Ru modification optimized the electronic structure and improved the conductivity of the cobalt metal-organic frameworks, thereby reducing the energy barrier of the rate-limiting step and accelerating the water splitting reaction.

N, S, P-Codoped Graphene-Supported Ag-MnFe2O4 Heterojunction Nanoparticles as Bifunctional Oxygen Electrocatalyst with High Efficiency

Due to slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharging and charging processes, it is essential to rationally design and synthesize non-precious metal bifunctional electrocatalysts with good performance for metal-air batteries. Herein, Ag-MnFe2O4 heterojunction nanoparticles supported on N, S, P-codoped graphene (NSPG) are developed with enhanced ORR and OER bifunctional electrocatalytic activities and stability. In contrast, S, P-doped graphene (SPG) and N, P-doped graphene (NPG) show less stabilization for the heterojunction particles. For example, under alkaline conditions, the ORR half-wave potential of Ag-MnFe2O4/NSPG can reach 0.831 V, and the over potential for OER is 0.56 V at the current density 10 mA·cm−2. Furthermore, Ag-MnFe2O4/NSPG shows better methanol resistance and durability than Pt/C catalysts.

Hierarchical MnCo2O4 nanowire@NiFe layered double hydroxide nanosheet heterostructures on Ni foam for overall water splitting

It is of great importance to construct non-precious metal bifunctional electrocatalysts with low cost and high efficiency for overall water splitting.

Nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

The oxygen reduction/evolution reactions (ORR/OER) are a key electrode process in the development of electrochemical energy conversion and storage devices, such as metal-air batteries and reversible fuel cells. The search for low-cost high-performance nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER alternatives to the widely-used noble metal-based catalysts is a research focus. This review aims to outline the opportunities and available options for these nanocarbon-based bifunctional electrocatalysts. Through discussion of some current scientific issues, we summarize the development and breakthroughs of these electrocatalysts. Then we provide our perspectives on these issues and suggestions for some areas in the further work. We hope that this review can improve the interest in nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER.

Atomically dispersed and nanoscaled Co species embedded in micro-/mesoporous carbon nanosheet/nanotube architecture with enhanced oxygen reduction and evolution bifunction for Zn-Air batteries

Developing active and stable non-precious metal bifunctional electrocatalysts towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) still remains a crucial challenge. Herein, we propose a simple strategy of integrating atomically dispersed and nanoscaled Co species embedded in micro-/mesoporous carbon nanosheet/nanotube architecture. Revealed by control and SCN- poisoning experiments, N species and atomically dispersed Co species are the main active centers for ORR; whereas the metal Co nanocrystals are the chief active species for OER. Additionally, the balanced micro/mesopore distribution offers fast mass diffusion, and carbon nanosheet/nanotube architecture supplies favorable 3D electrical conduct. As a result, the as-prepared CoNC (1:4) exhibits a positive half-wave potential of 0.87 V (vs RHE) for ORR, and a low potential of 1.55 V (vs RHE) at 10 mA cm−2 for the OER. Importantly, the flexible Zn-air battery using the catalyst exhibits a peak power density of 117 mW cm−2, a higher round-trip efficiency of 68% cycling at 2 mA/cm−2, and an excellent cycling stability with 3% decrease after 126 cycles test. This work provides a general strategy to design bifunctional catalysts by integrating atomically dispersed and nanoscaled transitional metal species together with N-doped micro-/mesoporous 3D carbon.

Al-doped nickel sulfide nanosheet arrays as highly efficient bifunctional electrocatalysts for overall water splitting.

The development of low-cost, high-activity, durable non-precious metal bifunctional electrocatalysts is of great importance in the production of hydrogen by water electrolysis. In this work, we have prepared new Al-doped Ni3S2 nanosheet arrays grown on Ni foam (Al-Ni3S2/NF) as an excellent bifunctional electrocatalyst in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Al-Ni3S2/NF electrode obtained only requires extremely low overpotentials of 86 and 223 mV for the HER and OER to achieve a current density of 10 mA cm-2 in 1 M KOH, respectively. Moreover, the electrolytic cell assembled using this electrode as both cathode and anode provides a current density of 10 mA cm-2 at an extremely low battery voltage of 1.58 V relative to that with Ni3S2/NF (1.71 V). Additionally, both experimental results and theoretical calculations reveal that the increased electrochemical active surface area and optimized intermediate adsorption free energies are responsible for the enhanced electrocatalytic performance. This work provides a promising bifunctional electrocatalyst for water electrolysis in alkaline media with broad application prospects.

Hollow ZnxCo1-xSe2 microcubes derived from Metal–Organic framework as efficient bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions

Electrocatalytic water splitting catalyst plays an important role in clean energy conversion system. Herein, we use [CH3NH3][ZnxCo1-x(HCOO)3] as precursors to prepare hollow ZnxCo1-xSe2 microcubes by a simple solvothermal strategy. Particularly, the synthesized hollow Zn0.1Co0.9Se2 microcube presents the best electrocatalytic performance, with a current density of 10 mA cm−2 at overpotential of only 196 mV for HER in acid and 308 mV for OER in alkaline solution, respectively. The hollow porous structure and a handful of zinc doping contribute to enhancing electrocatalytic performance. The former is conducive to expose more active sites, while the latter not only can improve the conductivity of the electrocatalyst, but also enhance the hydrogen adsorption capacity of the material. The synthesis method is simple, low toxicity and has no high temperature carbonization process, which provides a good prospect for the synthesis of non-precious metal bifunctional electrocatalysts with hollow structure.

Self-supported ternary (NixFey)2P nanoplates arrays as an efficient bifunctional electrocatalyst for overall water splitting

Developing non-precious metal bifunctional electrocatalysts for effective overall water splitting is promising to realize high-efficient renewable energy production. In this work, ternary (NixFey)2P nanoplates arrays on 3D self-supported nickel foams were prepared through a simple coelectrodeposition followed by phosphorization. The synthesized (NixFey)2P nanoplates arrays showed remarkable bifunctional electrocatalytic performances in the KOH electrolyte, with the Tafel slopes of 57.8 mV·dec−1 and 53.6 mV·dec−1, and low overpotentials of 115 mV and 182 mV to reach a current density of 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. In addition, the optimized (Ni0.66Fe0.33)2P anode and cathode demonstrated outstanding ability for overall water splitting in the two-electrode alkaline electrolyzer, generating a current density of 10 mA cm−2 at the applied cell voltage of 1.61 V. This benefited by the active surface to expedite reactants absorption, faster electron transport in the solid-liquid interface and reduced charge-transfer resistance due to the bimetallic synergistic effect. This delicate design of bifunctional transition metal phosphides provides a potential approach to realize water reuse and energy regeneration by the full water splitting.

Iron carbide encapsulated by porous carbon nitride as bifunctional electrocatalysts for oxygen reduction and evolution reactions

Herein, the study reports a facile and scale-up able strategy to synthesize metal organic frameworks (MOFs) Fe-7,7,8,8-Tetracyanoquinodimethane (Fe-TCNQ) as precursors to develop non-precious metal bifunctional electrocatalysts through a one-step hydrothermal route. Then, Fe3C/carbon nitride (Fe3C@CNx) core-shell structure composites are readily available through pyrolyzing Fe-TCNQ at reasonable temperature, during which hierarchical porous structures with multimodal porosity formed. Nitrogen doped porosity carbon layers can facilitate mass access to active sites and accelerate reaction. Consequently, the optimized catalyst exhibits superior oxygen reduction reaction (ORR) electrocatalytic activity and better catalytic activity for oxygen evolution reaction (OER) in alkaline medium than that of Pt/C, which can be attributed to the synergistic effect of strong coupling between Fe3C and nitrogen doped carbon shells, active sites Fe-NX, optimal level of nitrogen doping, and appropriate multimodal porosity.

Atomic‐Level Coupled Interfaces and Lattice Distortion on CuS/NiS2 Nanocrystals Boost Oxygen Catalysis for Flexible Zn‐Air Batteries

AbstractThe exploration of highly efficient nonprecious metal bifunctional electrocatalysts to boost oxygen evolution reaction and oxygen reduction reaction is critical for development of high energy density metal‐air batteries. Herein, a class of CuS/NiS2 interface nanocrystals (INs) catalysts with atomic‐level coupled nanointerface, subtle lattice distortion, and plentiful vacancy defects is reported. The results from temperature‐dependent in situ synchrotron‐based X‐ray absorption fine spectroscopy and electron spin resonance spectroscopy demonstrate that the lattice distortion of 14.7% in CuS/NiS2 caused by the strong Jahn–Teller effect of Cu, the strong atomic‐level coupled interface of CuS and NiS2 domains, and distinct vacancy defects can provide numerous effective active sites for their excellent bifunctional performance. A liquid Zn‐air battery with the CuS/NiS2 INs as air electrode displays a large peak power density (172.4 mW cm−2), a high specific capacity (775 mAh gZn−1), and long cycle life (up to 83 h), making the CuS/NiS2 INs among the best bifunctional catalysts for Zn‐air battery. More remarkably, the flexible CuS/NiS2 INs‐based solid‐state Zn‐air batteries can power the LED after twisting, making them be promising in portable and wearable electronic devices.

Controlling the Interfacial Environment in the Electrosynthesis of MnOx Nanostructures for High-Performance Oxygen Reduction/Evolution Electrocatalysis.

High-performance, nonprecious metal bifunctional electrocatalysts for the oxygen reduction and evolution reactions (ORR and OER, respectively) are of great importance for rechargeable metal-air batteries and regenerative fuel cells. A comprehensive study based on statistical design of experiments is presented to investigate and optimize the surfactant-assisted structure and the resultant bifunctional ORR/OER activity of anodically deposited manganese oxide (MnOx) catalysts. Three classes of surfactants are studied: anionic (sodium dodecyl sulfate, SDS), non-ionic (t-octylphenoxypolyethoxyethanol, Triton X-100), and cationic (cetyltrimethylammonium bromide, CTAB). The adsorption of surfactants has two main effects: increased deposition current density due to higher Mn2+ and Mn3+ concentrations at the outer Helmholtz plane (Frumkin effect on the electrodeposition kinetics) and templating of the MnOx nanostructure. CTAB produces MnOx with nanoneedle (1D) morphology, whereas nanospherical- and nanopetal-like morphologies are obtained with SDS and Triton, respectively. The bifunctional performance is assessed based on three criteria: OER/ORR onset potential window (defined at 2 and -2 mA cm-2) and separately the ORR and OER mass activities. The best compromise among these three criteria is obtained either with Triton X-100 deposited catalyst composed of MnOOH and Mn3O4 or SDS deposited catalyst containing a combination of α- and β-MnO2, MnOOH, and Mn3O4.The interaction effects among the deposition variables (surfactant type and concentration, anode potential, Mn2+ concentration, and temperature) reveal the optimal strategy for high-activity bifunctional MnOx catalyst synthesis. Mass activities for OER and ORR up to 49 A g-1 (at 1556 mVRHE) and -1.36 A g-1 (at 656 mVRHE) are obtained, respectively.

Fabrication and Bifunctional Electrocatalytic Performance of Ternary CoNiMn Layered Double Hydroxides/Polypyrrole/Reduced Graphene Oxide Composite for Oxygen Reduction and Evolution Reactions

It is of great and increasing interest to explore high-performance and low-cost bifunctional electrocatalysts towards oxygen reduction (ORR) and oxygen evolution reactions (OER) for fuel cell and water splitting systems. Herein, we fabricated ternary CoNiMn-Layered double hydroxides (LDH)/polypyrrole (PPy)/reduced graphene oxide (RGO) composite by one-step involving formation of the LDH and polymerization of the pyrrole (Py). Because of the synergistic effect among the different compositions, the prepared CoNiMn-LDH/PPy/RGO composite exhibits excellent bifunctional electrocatalytic activities with the lowest ΔE (EOER,10mAcm-2-EORR,–3mAcm-2) value of 0.85V among the non-precious metal bifunctional electrocatalysts as reported in the literatures, and good electrochemical durability for the ORR and the OER in alkaline media. The CoNiMn-LDH/PPy/RGO as one of non-precious metal electrocatalysts shows promising applications in a potential system for fuel cells and water splitting systems.

Three-dimensional metal-organic framework derived porous CoP3 concave polyhedrons as superior bifunctional electrocatalysts for the evolution of hydrogen and oxygen.

Developing low-cost and highly-efficient non-precious metal bifunctional electrocatalysts towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an attractively alternative strategy to solve the environmental pollution problems and energy demands. In this study, metal-organic framework (MOF) derived porous cobalt poly-phosphide (CoP3) concave polyhedrons are prepared and explored as superior bifunctional electrocatalysts for the HER and OER. The prepared MOF derived CoP3 concave polyhedrons show excellent electrocatalytic activity and stability towards the HER and OER in both acidic and alkaline media, with the Tafel slopes of 53 mV dec-1 and 76 mV dec-1 and a current density of 10 mA cm-2 at the overpotentials of -78 and 343 mV for the HER and OER, respectively, which are remarkably superior to those of the transition metal phosphides (TMPs) and comparable to those of the commercial precious metal catalysts. In addition, they also offer efficient catalytic activities and durabilities under neutral and basic conditions for the HER. The results of our study may shed light on the direction towards highly efficient bifunctional TMP electrocatalysts with high phosphorous component.