Bifunctional Electrocatalysts Research Articles

Ruthenium Nanoclusters and Single Atoms on α-MoC/N-Doped Carbon Achieves Low-Input/Input-Free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation.

The hydrazine oxidation-assisted H2 evolution method promises low-input and input-free hydrogen production. However, developing high-performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α-MoC/N-C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α-MoC nanoparticles-decorated N-doped carbon (α-MoC/N-C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring -80 mV and -9 mV respectively to reach 10 mA cm-2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H ad/desorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α-MoC/N-C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm-2 at just 64 mV. The zinc hydrazine (Zn-Hz) battery assembled with α-MoC/N-C/RuNSA cathode and Zn foil anode can exhibit 97.3 % energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn-Hz with OHzS system enables self-powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell-integrated-electrolyzer system.

Ruthenium Nanoclusters and Single Atoms on α‐MoC/N‐Doped Carbon Achieves Low‐Input/Input‐Free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation

AbstractThe hydrazine oxidation‐assisted H2 evolution method promises low‐input and input‐free hydrogen production. However, developing high‐performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α‐MoC/N−C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α‐MoC nanoparticles‐decorated N‐doped carbon (α‐MoC/N−C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring −80 mV and −9 mV respectively to reach 10 mA cm−2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H ad/desorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α‐MoC/N−C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm−2 at just 64 mV. The zinc hydrazine (Zn−Hz) battery assembled with α‐MoC/N−C/RuNSA cathode and Zn foil anode can exhibit 97.3 % energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn−Hz with OHzS system enables self‐powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell‐integrated‐electrolyzer system.

Engineering hierarchical snowflake-like multi-metal selenide catalysts anchored on Ni foam for high-efficiency and stable overall water splitting.

The development of excellent bifunctional electrocatalysts is an effective way to promote the industrial application of electrolytic water. In this work, a free-standing W-doped cobalt selenide (W-CoSe300/NF) electrocatalyst with a snowflake-like structure supported on nickel foam was prepared by a hydrothermal-selenization strategy. Benefiting from the high specific surface area of the 3D snowflake-like structure and the regulation of tungsten doping on the electronic structure of the metal active center, W-CoSe300/NF shows remarkable electrocatalytic water decomposition performance. In 1.0 M KOH, the W-CoSe300/NF electrocatalyst achieved an efficient HER and OER at a current density of 50 mA cm-2 with overpotentials as low as 84 mV and 283 mV, respectively. More importantly, W-CoSe300/NF acts as both the anode and cathode of the electrolytic tank, requiring only a potential of 1.54 V to obtain 10 mA cm-2 and can operate continuously for more than 120 hours at this current density. This study proposes a new way for the design of high efficiency and affordable bifunctional electrocatalysts.

Vanadium-Doped Heterogeneous Bimetallic Phosphides Derived from Layered Double Hydroxides for Saline Water Splitting.

The development of energy- and time-saving synthetic methods to prepare bifunctional and high stability catalysts are vital for overall water splitting. Here, V-doped nickel-iron hydroxide precursor by etching NiFe foam (NFF) at room temperature with dual chloride solution ("NaCl-VCl3"), is obtained then phosphating to obtain V-Ni2P-FeP/NFF as efficient bifunctional (oxygen/hydrogen exchange reaction, OER/HER) electrocatalysts, denoted as NFF(V, Na)-P. The NFF(V, Na)-P requires only 185 and 117 mV overpotentials to reach 10 mA cm-2 for OER and HER. When used as a catalyst for water splitting in a full cell, it can be stably sustained for more than 1000 h in alkaline brine electrolysis at both current densities of 100 and 500 mA cm-2. In situ Raman analyses and density functional theory (DFT) show that the V-doping-induced surface remodeling generates hydroxyl oxides as the true catalytic active centers, which not only enhances the reaction kinetics, but also reduces the free energy change in the rate-determining step. This work provides a cost-effective substrate self-derivation method to convert commercial NFF into a powerful catalyst for electrolytic brine, offering a unique route to the development of efficient electrocatalysts for saline water splitting.

Construction of RuO2-Ru/MoO2@carbon cloth bifunctional electrocatalyst for efficient overall water splitting

Construction of RuO2-Ru/MoO2@carbon cloth bifunctional electrocatalyst for efficient overall water splitting

ZIF-67-Derived Porous Carbon Nanosheets Decorated with Co Nanoflakes As Bifunctional Electrocatalysts for Overall Water Splitting

ZIF-67-Derived Porous Carbon Nanosheets Decorated with Co Nanoflakes As Bifunctional Electrocatalysts for Overall Water Splitting

One-step fabrication of P-Co5.47N/Co9S8@NPC heterojunction derived from saccharomycetes cerevisiae as environment-friendly bifunctional high-efficiency electrocatalysts

The one-step green preparation of heterojunction-structured bifunctional high-efficiency electrocatalysts provides a simple method for the green, low-cost, convenient and efficient application of hydrogen energy, meanwhile it is still challenging to achieve. In the present work, the phosphorus-doped two-phase heterojunction P-Co5.47N/Co9S8@NPC nanorods was synthesized on carbon cloth (CC) as a high-quality bifunctional electrode through simple one-step chemical vapor deposition (CVD) method. Saccharomycetes cerevisiae were used for the non-toxic phosphorus doping and formation of a carbon nanolayer wrapping Co5.47N/Co9S8 nanorods. Compared with the single-phase electrocatalyst Co9S8@NPC NSs/CC, P-Co5.47N/Co9S8@NPC NSs/CC exhibited more excellent electrocatalytic performance which required overpotentials of 69 mV for hydrogen evolution reaction (HER), 182.5 mV for oxygen evolution reaction (OER), 1.45 V for over water splitting (OWS) at 10 mA cm−2 in KOH solution. The designed P-Co5.47N/Co9S8@NPC NSs/CC presented multiple advantages of nanorod structure, doped structure, abundant heterointerfaces, as well as dual-phase synergy, which triggered outstanding electrocatalytic performance.

Transition Metal-Based Polyoxometalates for Oxygen Electrode Bifunctional Electrocatalysis

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec−1) value and the highest OER current density of 93.8 mA cm−2 were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with Rct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec−1 were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs.

Modulation in work function of CoTe as bifunctional electrocatalyst for rechargeable zinc air battery

The sluggish kinetics and inferior stability of oxygen electrocatalyst in rechargeable zinc air battery (ZAB) hamper its industrialization. In this work, we activate cobalt telluride (CoTe) by introduction of metallic cobalt (Co) to modulate the work function to facilitate the electron transfer from Co to CoTe during oxygen catalysis; additionally, the three-dimensional porous carbon nanosheets (3DPC) are invited to reduce the resistance towards electrolyte/oxygen diffusion. Thereby, Co-CoTe@3DPC only demands 280 mV overpotential to reach 10 mA cm−2 under alkaline oxygen evolution reaction (OER) condition, relatively lower than commercial iridium oxides (IrO2); besides the operando electrochemical impedance spectroscopy (EIS) indicates a better resistance towards surface reconstruction than Co@3DPC leading to a superior stability. A Pt-like oxygen reduction reaction (ORR) performance, half-wave potential associated with kinetic current density, is achieved for Co-CoTe@3DPC. A maximum power density of 203 mW cm−2 is achieved and sustains for 800 h. Furthermore, the all-solid-state ZAB offers 97 mW cm−2. Theoretical calculation suggests that the incorporation of metallic Co to CoTe maintains the superb ORR activity and promotes the OER catalysis.

Intermetallic ferric nickel silicide alloy derived from magadiite by magnesiothermic reaction as bifunctional electrocatalyst for overall water splitting

Intermetallic ferric nickel silicide alloy derived from magadiite by magnesiothermic reaction as bifunctional electrocatalyst for overall water splitting

Bimetallic Ni–Fe nanoparticles encapsulated with biomass-derived N-doped graphitic carbon core-shell nanostructures an efficient bifunctional electrocatalyst for enhanced overall seawater splitting and human urine electrolysis

Producing green hydrogen from abundant natural resources such as seawater and human urine is a viable solution for energy and industrial applications. However, the field of electrocatalysis faces challenges in developing cost-effective metal catalysts for efficient electrolysis of seawater and urea sewage. Here, we reported bimetallic NiFe nanoparticles encapsulated in a biomass derived N-doped graphitic carbon core shell structure (NiFe@BNGC-700) as a stable and effective catalyst for seawater and human urine electrolysis. NiFe@BNGC-700 exhibits remarkable electrocatalytic performance, with a low overpotential requiring 300 mV for OER and 297 mV for HER in alkaline 1.0 M KOH + seawater and 1.36 V for UOR in alkaline 1.0 M KOH + human urine at 50 mA cm−2 current density, respectively. The active bifunctional NiFe@BNGC-700 electrocatalyst symmetry pair facilitates the construction of a seawater electrolyser, achieving a cell voltage of 1.74 V at 50 mA cm−2 current density. Furthermore, the human urine-mediated electrolyser employing NiFe@BNGC-700//NiFe@BNGC-700 achieves a cell voltage of 1.64 V at the same current density, maintaining stability over 12 h with negligible potential deviation. Continual evolution of hydrogen and oxygen is feasible in a solar seawater a cell assembled with NiFe@BNGC-700 electrocatalyst, delivering at cell voltage of 1.74 V, enabling sustained and effective green hydrogen delivery on a large scale. This study proposes a sustainable strategy for fabricating electrodes consisting of non-precious metals, thereby permitting the economical and extensive generation of green hydrogen on a large scale.

Synergistic Pore Structure and Active Site Modulation in Co-N-C Catalysts Enabling Stable Zinc-Air Batteries.

Development of cheap, highly active, and durable nonprecious metal-based oxygen electrocatalysts is essential for metal-air battery technology, but achieving the balance of oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) bifunctional performance and long-term durability is still a great challenge. Using a typical Co-N-C catalyst as a model, herein, we introduced ammonium chloride into nitrogen-doped carbon materials containing metal elements during the pyrolysis process (Co-N-C/AC), which not only increases the active area but also realizes the accurate customization of the active site (pyridine nitrogen and cobalt oxide species) so as to achieve the balance of the OER/ORR bifunctional sites. The synthesized Co-N-C/AC bifunctional catalyst with a three-dimensional porous structure exhibits a smaller potential gap of 0.72 V. The peak power density of the aqueous cell at a current density of 308 mA cm-2 is 203 mW cm-2. The cycle life (≈3900 h) is longer than those of other recently reported aqueous Zn-air batteries (ZABs). The peak power density of the Co-N-C/AC-based quasi-solid-state ZAB reaches 550 mW cm-2 for ∼72 h. This work shows a feasible path for the practical application of ZABs by balancing the bifunctional electrocatalysts by tailoring the active site reasonably.

Metal-Organic-Framework-Derived Nitrogen-Doped Carbon-Matrix-Encapsulating Co0.5Ni0.5 Alloy as a Bifunctional Oxygen Electrocatalyst for Zinc-Air Batteries.

The development of low-cost, high-performance oxygen electrocatalysts is of great significance for energy conversion and storage. As a potential substitute for precious metal electrocatalysts, the construction of efficient and cost-effective oxygen electrocatalysts is conducive to promoting the widespread application of zinc-air batteries. Herein, CoxNiyMOF nanoparticles encapsulated within a carbon matrix were synthesized and employed as cathode catalysts in zinc-air batteries. Co0.5Ni0.5MOF exhibits superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance and durability. The zinc-air battery assembled with Co0.5Ni0.5MOF as the air cathode exhibits a maximum power density of 138.6 mW·cm-2. These improvements are mainly attributed to the optimized metal composition of the cobalt-nickel alloy, which increases the specific surface area of the material and optimizes its pore structure. Significantly, the optimization of the electronic structure and active sites within the material has led to amplified ORR/OER activity and better zinc-air battery performance. This study underscores the immense promise of Co0.5Ni0.5MOF catalysts as feasible substitutes for commercial Pt/C catalysts in zinc-air batteries.

Atomic Engineering of 3D Self‐Supported Bifunctional Oxygen Electrodes for Rechargeable Zinc‐Air Batteries and Fuel Cell Applications

AbstractThe oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are cornerstone half reactions involved in many renewable energy technologies. High‐density single‐atom catalysts maximize the atom utilization and isolated active sites. Furthermore, introduction of pyri‐N into the carbon‐based nanostructures as an oxygen electrocatalyst creates an abundance of active sites. Here, an innovative strategy is reported based on atomic scale dispersion of Co atoms into the pyri‐N enriched carbon nanotube encapsulated Ni nanoparticles grown on 3D electrospun carbon nanofiber nano‐assemblies. Notably, the CoSANi‐NCNT/CNF electrocatalyst exhibited excellent OER and ORR activity in terms of low overpotentials and higher half‐wave potentials. The atomically distributed Co allows the maximum exposure of active sites on the pyri‐N dominated multidimensional carbon skeleton, and synergistic effects with Ni nanoparticles greatly reduced the delocalization around the metal centers and provided an ideal environment for interactions with oxygen intermediates, thus facilitating the 4e− pathway, as evidenced by the DFT calculations. Moreover, Zn‐air batteries using a CoSANi‐NCNT/CNF air cathode exhibited a high‐power density and admirable specific capacity. This studies may provide an avenue for the rational modulation of single‐atom catalysts and cost‐effective, large‐scale synthesis of bifunctional oxygen electrocatalysts for rechargeable Zn‐air batteries and anion exchange membrane fuel cell.

Three-dimensional Cobalt-MOF/ CNF microstructured assembly as a bifunctional electrocatalyst for effective overall water-splitting in alkaline media

The electrocatalyst Co-MOF/CNF microstructure exhibits excellent stability and charge transfer efficiency synthesized via ultrasonication technique. The composite has a lower Rct value of 2 Ω. The larger Cdl value of Co-MOF/CNF (12.3 mF/dec) is responsible for the high catalytic activity for both HER and OER reactions. The composite has strong catalytic activity in HER and OER, with low overpotentials of 193 mV and 250 mV at 10 mA/cm2. Furthermore, excellent water electrolyzer activity was achieved by Co-MOF/CNF||Co-MOF/CNF with a cell voltage of 1.49 V at 10 mA/cm2 and is stable over 24 h, proving the long-term efficacy in sustainable energy systems.

Hydrothermal synthesis of high-performance cobalt phosphate nanorod architecture as bifunctional electrocatalysts for rechargeable Zn-air batteries and supercapatteries

Transition metal phosphate bifunctional electrocatalysts demonstrate superior oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and capacitive properties owing to their high electrocatalytic and conductive activities. In this report, cobalt phosphate (Co3P2O8) nanorod (NR) electrocatalytic materials were developed via a facile one-step hydrothermal synthesis, followed by an annealing process. The unique NR structures offer superior electrocatalytic activities, continuous and quick electron transport pathways, short ion diffusion lengths, and rich active sites toward rechargeable zinc-air batteries (ZABs) and supercapatteries (SCs). The self-assembled Co3P2O8 NR electrocatalyst revealed higher current density values during the OER and ORR measurements than the commercially available Pt/C and IrO2 materials. The Co3P2O8 NR electrocatalyst exhibited an excellent OER overpotential of 180 mV. The electocatalyst also showed superior onset and half-wave potentials of 0.92 V and 0.80 V, respectively. Moreover, the fabricated Co3P2O8 NRs-based ZAB exhibited better durability than the Pt/C-based ZAB. Significantly, the Co3P2O8 NR electrode demonstrated an excellent specific capacity of 373 mAh g−1 with outstanding cycling stability of 99% after 5000 cycles. Additionally, the fabricated Co3P2O8 NRs//activated carbon SC demonstrated high specific energy and power densities of 25.62 Wh kg−1 and 2953.12 W kg−1, respectively with remarkable cycling stability of 89% after 7000 cycles. Specifically, the practical applicability of the fabricated Co3P2O8 NRs-based ZAB and SC was tested using a blue light-emitting diode nameplate energized by two devices in series. Overall, the catalytic and energy-storage properties of the Co3P2O8 NR material can provide a new pathway for high-energy electrochemical applications.

Covalent organic framework‐derived Fe, Co‐nitrogen codoped carbon as a bifunctional electrocatalyst for rechargeable efficient Zn–air batteries

Covalent organic framework‐derived Fe, Co‐nitrogen codoped carbon as a bifunctional electrocatalyst for rechargeable efficient Zn–air batteries

MoOx/CoMo on Cu nanowires as an efficiently bifunctional electrocatalyst for overall water splitting

Electrocatalytic water splitting is a promising approach for sustainable hydrogen production. The design and development of efficient and stable bifunctional catalysts are the key to realizing hydrogen production from water splitting. Herein, we successfully synthesized bifunctional MoOx/CoMo grown on copper nanowires (Cu NWs) through an electrodeposition approach, showing excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. The MoOx/CoMo/Cu NWs catalyst exhibited overpotentials as low as 56 mV and 211 mV to deliver a current density of 10 mA cm‐2 for HER and OER in alkaline media, respectively. Moreover, the MoOx/CoMo/Cu NWs as bifunctional electrodes for overall water splitting achieved a low voltage of 1.45 and 1.62 V at 10 and 50 mA cm‐2, respectively, with a stability of 10 h at 50 mA cm‐2. This work provides a promising strategy for designing highly active catalysts that replace precious‐metal‐based catalysts on energy conversion.

Coupling of modulating d-band center and optimizing interface electronic structure via MXene and Bi-metal doping in CoP achieving efficient bifunctional catalytic activity for water splitting

Bifunctional electrocatalysts that exhibit excellent catalytic activity for both hydrogen (HER) and oxygen evolution reactions (OER) are ideal for alkaline overall water splitting. The unique structure and diverse composition of cobalt phosphide catalysts are highly favorable for enhancing catalytic reaction kinetics. However, cobalt phosphide electrocatalysts typically exhibit insufficient OER activity. To overcome this text, we synthesized a Ru and V co-doped CoP-coupled highly conductive MXene catalyst with nano-arrays by in-situ growth on the surface of carbon cloth. The HER and OER overpotentials of the catalyst at 10 mA cm−2 current density were 30 and 206 mV, respectively. Furthermore, a series of physicochemical characterizations and first-principles calculations demonstrated that the increased HER and OER activities resulted from the synergistic effect established by the double doping and heterostructure. This effect produced an effective modulation of the d-band center of the catalysts, promoting adsorption effects on the intermediates. In conclusion, this work presents a novel approach to improving the electrocatalytic activity of phosphides and provides a faster and more environmentally friendly method for separating hydrogen from water.

Heterostructure catalyst coupled wood-derived carbon and cobalt-iron alloy/oxide for reversible oxygen conversion

As promising energy-storage devices, zinc–air batteries (ZABs) exhibit slow reaction kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurring at their electrodes. High-performance bifunctional catalysts must thus be synthesized to accelerate the reversible conversion of oxygen and improve the rate and overall performance of ZABs. Herein, we reported the promising prospects of self-supported composite electrodes composed of wood-derived carbon (WDC) and bimetallic cobalt-iron alloys/oxides (CoFe-CoFe2O4@WDC) as efficient electrocatalysts for alkaline ORR/OER. WDC provided a favorable three-phase interface for heterogeneous reactions owing to its layered porous structure and genetic stability, thereby enabling mass diffusion and improving reaction kinetics. The CoFe2O4 spinel surface was reduced to bimetallic CoFe alloy to form abundant heterostructure interfaces that promote electron transfer. Under alkaline conditions, the optimized composite electrode exhibited a remarkable high half-wave potential of 0.85 V and an exceptionally low overpotential of 1.49 V. It also exhibited stable performance over an impressive 2340 cycles in a ZAB. Theoretical calculations also confirmed that the heterointerface addresses the issue of proton scarcity throughout the reaction and actively facilitates the creation of O–O bonds during the reversible transformation of oxygen. This study introduces a new concept for developing bifunctional and efficient electrocatalysts based on charcoal and encourages the sustainable and high-value use of forest biomass resources.Graphical