Electrode Catalyst Research Articles

Revealing the Role of Mo Leaching in the Structural Transformation of NiMo Thin Film Catalysts upon Hydrogen Evolution Reaction.

NiMo alloys are considered highly promising non-noble Hydrogen Evolution Reaction (HER) catalysts. Besides the synergistic effect of alloying elements, recent attention is drawn to the Mo leaching from the catalyst. This work investigates the role of Mo in NiMo alloys during HER, aiming to understand the interplay between compositional, structural, and electronic factors on the activity, and their effects on the electrode material and catalyst properties. For this purpose, sputter-deposited low roughness NixMo100-x thin films are produced. The investigation of catalyst performance depending on their chemical composition shows a volcano-shaped plot, peaking for the Ni65Mo35 alloy with the highest intrinsic activity in alkaline HER. A comprehensive electrode surface analysis combining transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy identifies the leaching of Mo on a structural level and indicates the formation of a Ni(OH)2-rich surface area. The ultimate surface characteristics of the NiMo catalysts depend on the initial composition and the electrochemical procedure. Based on the findings, it conclude that the observed catalytic properties of NiMo alloys in HER are determined by a complex interplay of increasing roughness, available surface species and their synergies. The leaching of Mo has a proven structural effect and is considered one of several factors contributing to the enhanced catalyst activity.

Textile-Based Membraneless Microfluidic Double-Inlet Hybrid Microbial-Enzymatic Biofuel Cell.

This study reports the development of a textile-based colaminar flow hybrid microbial-enzymatic biofuel cell. Shewanella MR-1 was used as a biocatalyst on the anode, and bienzymatic system catalysts based on glucose oxidase and horseradish peroxidase were applied on an air-breathing cathode to address the overpotential loss in a body-friendly way. A single-layer Y-shaped channel configuration with a double-inlet was adopted. Microchannels of biofuel cells were patterned by silk screen printing with Ecoflex to maintain the flexibility of textile substrates without harm to the human body. The electrodes were fabricated with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and a mixture of multiwalled carbon nanotubes and single-walled carbon nanotubes by screen printing. The effects of electrode materials, catalyst type, catalyst concentration, and glucose concentration in the catholyte were investigated to optimize the fuel cell performance. The peak power density (44.9 μW cm-2) and maximum current density (388.9 μA cm-2) of the optimized hybrid biofuel cell were better than those of previously reported textile- or paper-substrate microscale single microbial fuel cells. The developed biofuel cell will be a useful platform as a microscale power source that is harmless to the environment and living organisms.

Boosted electrocatalytic activity and durability of Cu[sbnd]Fe/N[sbnd]C by modulating the interfacial composition and electronic structure for efficient oxygen reduction reaction

Oxygen reduction reaction (ORR) serves as the foundation for various electrochemical energy storage devices. Fe/NC catalysts are expected to replace commercial Pt/C as oxygen electrode catalysts based on the structural tunability at the atomic level, abundant iron ore reserves and excellent activity. Nevertheless, the lack of durability and low active site density impede its advancement. In this work, a durable catalyst, CuFe/NC, for ORR was prepared by modulating the interfacial composition and electronic structure. The introduction of Cu nanoclusters partially eliminates the Fenton effect from Fe and optimizes the electron structure of FeNx, thereby effectively enhancing the long-term durability and activity. The prepared CuFe/NC exhibits a half-wave potential (E1/2) of 0.90 V and superior stability with a decrease in E1/2 of only 20 mV after 10,000 cycles. The assembled alkaline Zinc-Air batteries (ZABs) with CuFe/NC exhibit an open-circuit potential of 1.458 V. At a current density of 5 mA cm−2, the batteries are capable of operation for 600 h with a stable polarization. This CuFe/NC may promote the practical application of novel and renewable electrochemical energy storage devices.

Mechanochemically synthesized RuO2‐doped LaMnO3 perovskites as bifunctional cathodes for rechargeable Zn/air batteries

Herein, we have developed LaMnO3 (LMO) perovskite‐based electrocatalysts of oxygen reduction and oxygen evolution reactions (ORR and OER) in a basic aqueous solution. Mechanochemical grinding and thermal annealing leads to highly‐pure perovskites as shown by X‐ray diffraction. This methodology allows as well for a swift integration of RuO2 additive which improves especially the oxygen evolution reaction. ORR have been analyzed by rotating ring‐disk electrode (RRDE). Eventually, these catalysts are employed in Zn/air batteries resulting in specific capacity values of 12.76 Ahg‐1 at 1 Ag‐1, when LMO‐RuO2 (LMO‐Ru) was used as catalyst in the positive electrodes. Besides, high operational stability of Zn/air batteries for over 100 cycles was obtained, saving 1,46 mWh per cycle when LMO‐Ru was used with respect to pure LMO.

Synthesis of MS2 (M=Mo, W) thin films by chemical solution deposition

MoS2 and WS2 as typical two-dimensional transition metal dichalcogenides have been investigated since of rich physicochemical properties. To deposit MoS2 and WS2 thin films, chemical solution deposition as a facile route had been used showing the advantages of high component controllability, low cost, sequential processing of device, easy preparation of large-size films and facile preparation of films on irregular substrates. Here, Mo1-xWxS2 (0 ≤ x ≤ 1) thin films were successfully prepared by chemical solution deposition method. The phases as well as microstructures were investigated using field emission scanning electron microscope, atomic force microscopy, transmission electron microscopy, Raman and x-ray photoelectron spectroscopy measurements. The prepared Mo1-xWxS2 thin films are used as hydrogen evolution reaction (HER) catalyst electrodes for water splitting. The Mo0·3W0·7S2 thin film catalyst shows an overpotential of 345 mV at a current density of 10 mA cm−2 and the corresponding Tafel slope of 169 mV dec−1 in 0.5 M sulfuric acid. The results will provide a facile method to deposit MX2 thin films.

N/S‐Doped Hierarchical Porous Bamboo Carbon Fibers with Ultra‐Large Surface Area and Highly Exposed Active Sites for Flexible Zinc‐Air Battery†

Comprehensive SummaryFacile mass transport channel and accessible active sites are crucial for binder‐free air electrode catalysts in rechargeable flexible zinc‐air battery (ZAB). Herein, a ZnS/NH3 dual‐assisted pyrolysis strategy is proposed to prepare N/S‐doped hierarchical porous bamboo carbon cloth (HP‐NS‐BCC) as binder‐free air electrode catalyst for ZAB. BCC fabric with abundant micropores is firstly used as flexible carbon support to facilitate the heteroatom‐doping and construct the hierarchical porous structure. ZnS nanospheres and NH3 activization together facilitate the electronic modulation of carbon matrix by N/S‐doping and optimize the macro/meso/micropores structure of carbon fibers. Benefiting from the highly‐exposed N/S‐induced sites with enhanced intrinsic activity, the optimized mass transport of biocarbon fibers, as well as the ultra‐large specific surface area of 2436.1 m2·g–1, the resultant HP‐NS‐BCC catalyst exhibits improved kinetics for oxygen reduction/evolution reaction. When applied to rechargeable aqueous ZABs, it achieves a significant peak power density of 249.1 mW·cm−2. As binder‐free air electrode catalyst, the flexible ZAB also displays stable cycling over 500 cycles with a minimal voltage gap of 0.42 V, showcasing promising applications in flexible electronic devices.

Study on the electrodeposition of MoS2 on different electrode materials used as electrode catalysts for the electrochemical synthesis of ammonia from N2 and H2O

Herein, MoS2 was deposited electrochemically on nickel foam (NF), copper foam (CuF) and carbon paper (CP). The samples were characterized by XRD, SEM and were used as cathodes for the nitrogen reduction reaction in an acidic medium. NH4+ concentration was determined by the indophenol blue method. Both the density of the cathodic current and the NH4+ concentration achieved their highest values with MoS2 deposited on copper foam. However, nickel foam was determined to be a higher-performance electrode material, which showed highest NRR efficiency, 3,62%, probably due to its higher ECSA value.

Density Functional Theory Calculations to Increase the Efficiency of Oxygen Electrode Catalysts from Ytterbium Single Atom Catalysts Using Nitrogen Solid Supports

Density Functional Theory Calculations to Increase the Efficiency of Oxygen Electrode Catalysts from Ytterbium Single Atom Catalysts Using Nitrogen Solid Supports

Nitrogen-doped mesoporous carbon combined with carbon nanotubes as counter electrode catalysts for quantum dot sensitized solar cells with record efficiency

The fabrication of a counter electrode possessing elevated catalytic efficiency and steadfast stability is a crucial prerequisite for the high-performance quantum dot sensitized solar cells (QDSCs). Mesoporous carbon (MC) has been adopted as the desired CE material in the past years, but the disadvantage of its poor conductivity has limited further development of the performance of QDSCs. In this study, we present a straightforward approach for producing highly effective counter electrodes through the integration of nitrogen-doped mesoporous carbon (N-MC) with carbon nanotubes (CNTs), forming a composite material that is deposited onto a titanium mesh substrate. The counter electrode (CE) based on composite materials shows excellent electrocatalytic performance, synergistically benefiting from large specific areas of N-MC and high conductivity of CNTs. Electrochemical measurements reveal that the optimal CEs exhibit excellent catalytic reduction activity as well as high electron mobility. Consequently, the corresponding QDSCs show a record power conversion efficiency of 16.68 %.

Quantitative study of oxygen evolution reaction using LiNi0.5Mn1.5O4 thin-film electrodes

The development of water electrolysis catalysts that accelerate the oxygen evolution reaction (OER) is a crucial challenge. Ni-based oxides are promising OER catalysts; however, quantitative studies of Ni-based oxides remain unexplored. In this study, we quantitatively evaluated the OER activity of LiNi0.5Mn1.5O4 as a thin-film electrode catalyst. The LiNi0.5Mn1.5O4 thin film fabricated using a sputtering method exhibited a current density of 6.6 and ∼2.6 mAcm−2 for geometric and estimated areas, respectively, at 1.78 V vs. a reversible hydrogen electrode. X-ray photoelectron spectroscopy indicated the presence of Ni3+ in the as-grown and post-OER LiNi0.5Mn1.5O4 thin films. These results suggest that Ni3+ plays a key role in the OER of LiNi0.5Mn1.5O4.

Electrocatalysis in Solid Oxide Fuel Cells and Electrolyzers.

Interest in energy-to-X and X-to-energy (where X represents green hydrogen, carbon-based fuels, or ammonia) technologies has expanded the field of electrochemical conversion and storage. Solid oxide electrochemical cells (SOCs) are among the most promising technologies for these processes. Their unmatched conversion efficiencies result from favorable thermodynamics and kinetics at elevated operating temperatures (400-900 °C). These solid-state electrochemical systems exhibit flexibility in reversible operation between fuel cell and electrolysis modes and can efficiently utilize a variety of fuels. However, electrocatalytic materials at SOC electrodes remain nonoptimal for facilitating reversible operation and fuel flexibility. In this Review, we explore the diverse range of electrocatalytic materials utilized in oxygen-ion-conducting SOCs (O-SOCs) and proton-conducting SOCs (H-SOCs). We examine their electrochemical activity as a function of composition and structure across different electrochemical reactions to highlight characteristics that lead to optimal catalytic performance. Catalyst deactivation mechanisms under different operating conditions are discussed to assess the bottlenecks in performance. We conclude by providing guidelines for evaluating the electrochemical performance of electrode catalysts in SOCs and for designing effective catalysts to achieve flexibility in fuel usage and mode of operation.

Effect of gas diffusion layer surface property on platinum nanowire array electrode performance in proton exchange membrane fuel cells

3D-ordered catalyst electrodes have been recognized as one effective strategy to reach high current density operation for proton exchange membrane fuel cell (PEMFC) applications. Gas diffusion electrodes (GDEs) with platinum nanowire arrays in-situ grown on gas diffusion layer (GDL) surface is an important contribution in this area, but the performance is highly dependent on the GDL surface properties. In this study, the GDLs available in the market are systematically investigated, with a focus on the influence of the GDL surface properties on the in-situ growth of Pt nanowire arrays to fabricate GDEs as cathodes for PEMFCs. The experimental results indicate that mesopores especially micropores play a key role. They enable a hydrophilic surface for the isopropanol pretreated GDL, facilitating the in-situ growth of Pt nanowires to form a uniform array with a large electrochemical surface area (ECSA), finally leading to a high-power density. With Freudenberg H24CX483 carbon paper GDL, the highest power density of 0.9 W cm−2 is achieved. The understanding achieved here could be further used to develop novel GDLs for fabricating the next generation of electrodes for large current density operations.

Highly active air electrode catalysts for Zn‐air batteries: Catalytic mechanism and active center from obfuscation to clearness

AbstractCarbon‐based materials have been found to accelerate the sluggish kinetic reaction and are largely subject to the overall Zn‐air batteries (ZABs) property, while their full catalytic mechanism is still not excavated because of the indistinct internal structure and immature in‐situ technology. Up to now, systematic methods have been utilized to study and design promising high‐performance carbon‐based catalysts. To resolve the real active units and catalytic mechanism, developing molecular catalyst is a significant strategy. Herein, the review will initiate to briefly introduce the working principle and composition of ZABs. An important statement is correspondingly provided about the typical structure and catalytic mechanisms for the air cathode material. It also presents the tremendous endeavors on the catalytic performance and stability of carbon‐based material. Furthermore, combined with theoretical calculation, the self‐defined active sites are analyzed to understand the catalytic character, where the molecular catalyst is subsequently summarized and discussed through highlighting the unambiguous and controllable structure, in the hope of surfacing the optimum catalyst. Building on the fundamental understanding of carbon‐based and molecular catalysts, this review is expected to provide guidance and direction toward designing future mechanistic studies and ORR electrocatalysts.

Co/Ce-MOF-Derived Oxygen Electrode Bifunctional Catalyst for Rechargeable Zinc-Air Batteries.

Improving the practicality of rechargeable zinc-air batteries relies heavily on the development of oxygen electrode catalysts that are low-cost, durable, and highly efficient in performing dual functions. In the present study, a catalyst with atomic Ce and Co distribution on a nitrogen-doped carbon substrate was prepared by doping the rare earth elements Ce and Co into a metal-organic framework precursor. Rare earth element Ce, known for its unique structure and excellent oxygen affinity, was utilized to regulate the catalytic activity. The catalyst prepared in this study demonstrated an exceptional electrocatalytic performance. At a current density of 10 mA cm-2, the catalyst exhibited an overpotential of 340 mV for the oxygen evolution reaction (OER), which was lower than that of commercial IrO2 (370 mV), while achieving a half-wave potential of 0.79 V for the process of oxygen reduction reaction (ORR), exhibiting a similar level of effectiveness as commercially accessible Pt/C catalysts (0.8 V). The catalyst's porous structure, interconnected three-dimensional carbon network, and large specific surface area are the factors contributing to the significant improvement in catalytic performance. Furthermore, in comparison to commercial Pt/C+IrO2, the catalyst exhibited good cycling stability and high efficiency in rechargeable zinc-air batteries.

Design and construction of MoS2/Ni3S2 nanosheets decorated on multi-walled carbon nanotubes as a sustainable counter electrode for dye-sensitized solar cells: An experimental and computational investigation

To achieve a satisfactory photovoltaic performance in dye-sensitized solar cells (DSSCs), counter electrode (CE) catalysts with low cost, superior catalytic activity and excellent conductivity should be developed. Herein, we successfully prepared the MoS2/Ni3S2 heterostructures via the hydrothermal method and decorated on multi-walled carbon nanotubes (MWCNTs) by sonication method. The performance of the prepared CEs was investigated by various electrochemical techniques. Based on the electrochemical tests, the MoS2/Ni3S2/MWCNTs ternary nanocomposite displayed high electron transfer ability, remarkable catalytic activities, and good stability in the I3−/I− electrolyte. The power conversion efficiency (PCE) of DSSCs based on MoS2/Ni3S2/MWCNTs CE reached 8.27 %, which was even higher than that of the DSSC with Pt CE (7.23 %). The excellent performance of the catalyst is related to the structural properties, synergistic effect of MoS2/Ni3S2 and MWCNTs, and high porosity of MoS2/Ni3S2/MWCNTs composite. The results of calculations indicated that by decorating the MoS2/Ni3S2 on carbon nanotubes (CNTs), the bandgap decreased to 2.79 eV, which was smaller than the individual CNTs (6.27 eV). This finding depicted that synergistic effect between MoS2/Ni3S2 and MWCNTs can reduce the bandgap of MoS2/Ni3S2/MWCNTs composite. The lower bandgap mostly results in higher electrical conductivity and lower charge-transfer resistance, which plays an important role in improving the efficiency of DSSCs.

Chemical Doping and O-Functionalization of Carbon-Based Electrode to Improve Vanadium Redox Flow Batteries.

The vanadium redox flow battery (VRFB) holds promise for large-scale energy storage applications, despite its lower energy and power densities compared to advanced secondary batteries available today. Carbon materials are considered suitable catalyst electrodes for improving many aspects of the VRFB. However, pristine graphite structures in carbon materials are catalytically inert and require modification to activate their catalytic activity. Among the various strategies developed so far, O-functionalization and chemical doping of carbon materials are considered some of the most promising pathways to regulate their electronic structures. Building on the catalytic mechanisms involved in the VRFB, this concise review discusses recent advancements in the O-functionalization and chemical doping of carbon materials. Furthermore, it explores how these materials can be tailored and highlights future directions for developing more promising VRFBs to guide future research.

Synergistic role of MoS2 in gelation-induced fabrication of graphene oxide films.

Supporting materials for electrocatalysts must exhibit relative chemical inertness to facilitate unimpeded movement of gas, and demonstrate electrical conductivity to promote efficient electron transfer to the catalyst. Conventional catalyst electrodes, such as glassy carbon, carbon cloths, or Ni foam, are commonly employed. However, the challenge lies in the limited stability observed during testing due to the relatively weak adhesion between the catalyst and the electrode. Addressing this limitation is crucial for advancing the stability and performance of catalyst-electrode systems in various applications. Here, we suggest a novel fabrication method for a freestanding conducting film, accomplished through gelation, incorporating 1T-MoS2 and graphene oxide. 1T-MoS2 nanosheets play a crucial role in promoting the reduction of graphene oxide (GO) on the Zn foil. This contribution leads to accelerated film formation and enhanced electrical conductivity in the film. The synergistic effect also enhances the film's stability as catalyst supports. This study provides insights into the effective utilization of MoS2 and graphene oxide in the creating of advanced catalyst support systems with potential applications in diverse catalytic reaction.

3D printed CuFe2O4 electrode with dominant facet (111) for boosting hydrogen evolution performance

The utilization of hydrogen energy is an important way to low carbon economy, and the development of active electrodes is the most critical step for efficient hydrogen evolution reaction. With the addition of KNO3 as a capping agent, the exposed crystal facet of CuFe2O4 is regulated, and the crystal facet (111) becomes dominant. Compared to CuFe2O4 (3 1 1), CuFe2O4 (111) exhibits low barrier of water dissociation and suitable *H binding strength, resulting in high intrinsic activity. Furthermore, the 3D printed electrodes show more excellent performance. At 3D printed CuFe2O4 (111) electrode, the overpotential is only 152 mV (vs. reversible hydrogen electrode) at 100 mA cm−2, and Tafel slope is as low as 33 mV dec-1. In addition, 3D printed CuFe2O4 (111) electrodes shows high stability. The superior performance of 3D printed CuFe2O4 (111) electrodes originates from high intrinsic activity and more exposed active sites. This study provides a new path for the development of efficient, stable and inexpensive monolithic catalyst electrodes for alkaline hydrogen evolution.

Preparation of Oxygen Reduction Catalyst Electrodes by Electrochemical Acidification and Synergistic Electrodeposition

A proton exchange membrane fuel cell (PEMFC) is an efficient and environmentally friendly power production technology that uses hydrogen energy. The cathodic oxygen reduction electrode is a critical component in the development of PEMFC. Most techniques deposit catalyst nanoparticles in areas that are inaccessible for catalytic processes, reducing platinum utilization. The substrate used in this study was carbon paper (CP) with a self-supporting structure. First, electrochemical acidification technology was employed to modify the CP’s surface, followed by nanoparticle manufacturing and fixation on the CP in a single step by electrodeposition. The Pt/C0.5V2.24CP catalyst electrode demonstrated high-quality activity in the oxygen reduction reaction (ORR), with a homogeneous particle dispersion and particle size of around 50 nm. The mass activity and electrochemical active surface area (ECSA) of the Pt/C0.5V2.24CP catalyst electrode were 1.74 and 3.98 times higher than those of the Pt/C/CP-1 electrodes made with commercial catalysts, respectively. After 5000 cycles of accelerated durability testing (ADT), the mass activity and ECSA were 1.28 times and 6.16 times more than Pt/C/CP-1. This paper successfully proved the viability of electrodepositing Pt nanoparticles on CP following acidification, and that the electrochemical acidification methods have a positive influence on improving electrode ORR activity.

Electrode catalyst for fuel cell, and fuel cell using same

Electrode catalyst for fuel cell, and fuel cell using same