High-performance Cathode Catalyst Research Articles

Porous Ruthenium-Tungsten-Zinc Nanocages for Efficient Electrocatalytic Hydrogen Oxidation Reaction in Alkali.

With the rapid development of anion exchange membrane technology and the availability of high-performance non-noble metal cathode catalysts in alkaline media, the commercialization of anion exchange membrane fuel cells has become feasible. Currently, anode materials for alkaline anion-exchange membrane fuel cells still rely on platinum-based catalysts, posing a challenge to the development of efficient low-Pt or Pt-free catalysts. Low-cost ruthenium-based anodes are being considered as alternatives to platinum. However, they still suffer from stability issues and strong oxophilicity. Here, we employ a metal-organic framework compound as a template to construct three-dimensional porous ruthenium-tungsten-zinc nanocages via solvothermal and high-temperature pyrolysis methods. The experimental results demonstrate that this porous ruthenium-tungsten-zinc nanocage with an electrochemical surface area of 116 m2 g-1 exhibits excellent catalytic activity for hydrogen oxidation reaction in alkali, with a kinetic density 1.82 times and a mass activity 8.18 times higher than that of commercial Pt/C, and a good catalytic stability, showing no obvious degradation of the current density after continuous operation for 10,000 s. These findings suggest that the developed catalyst holds promise for use in alkaline anion-exchange membrane fuel cells.

Ultrathin Ni–N–C layer modified Pt–Ni alloy nanoparticle catalysts for enhanced oxygen reduction

Accelerating the commercialization of fuel cells requires the development of Pt-based alloy cathode catalysts with high ORR operation, low price, and excellent reliability. However, it is a challenging task to fabricate uniformly dispersed, low-loaded, and small-sized Pt-based alloy catalysts to resolve the contradiction between activity and stability. Here, sub-3 nm N-doped PtNi nanoparticles (NPs) are synthesized as high-performance PEMFC cathode catalysts. PtNi/Ni-NC exhibits excellent electrocatalytic activity (0.51 A mgPt−1@0.8 V and peak power density of 328 mW cm−2) as well as stability (only 15 mV loss in E1/2 after 5000 cycles of ADT tests) in oxygen reduction reaction (ORR). The experimental results show that N doping modulates the electronic structure around Pt and optimizes the lattice compressive strain, thus attenuating the adsorption of oxygen intermediates on the surface Pt and enhancing the ORR activity. Meanwhile, the encapsulation of PtNi NPs by the constructed ultrathin Ni–N–C layer accounts for the improved stability. This work offers a novel perspective f for raising the stability and catalytic performance of Pt-based catalysts.

A novel binder-free cathode catalyst Cu@NCNF/CP with three-dimensional self-supporting structure for Li-CO2 battery

The Li-CO2 battery is an emerging energy storage device that has garnered significant attention due to its high theoretical energy density and remarkable CO2 capture ability. However, the low reaction activity of Li2CO3 formation and decomposition may result in large overpotentials and poor cycling performance. In this work, a novel three-dimensional self-supporting high-performance cathode catalyst (Cu@NCNF/CP) was prepared. The Cu@NCNF/CP cathode catalyst is composed of Cu nanoparticles loaded on nitrogen-doped carbon nanotube fibers (NCNF) deposited on carbon paper (CP). The three-dimensional interconnected self-supporting structure of Cu@NCNF/CP eliminates the need for binders and can facilitate efficient electrolyte diffusion and electron transfer. Moreover, the nitrogen doping introduces enrichment active sites, and boosts the CO2 reduction reaction (CO2RR) activity, while the uniformly loaded Cu nanoparticles facilitate the adsorption and precipitation of CO2 molecules, thereby playing a crucial role in enhancing the electrocatalytic activity of the CO2 evolution reaction (CO2ER). Importantly, the Li-CO2 battery utilizing Cu@NCNF/CP as a cathode catalyst exhibits a large discharge capacity of 10.59 mAh cm−2 at a current density of 0.05 mA cm−2. When the cutoff capacity is limited to 0.15 mAh cm−2, the first-cycle overpotential is merely 1.28 V, and the cycle life can reach 1140 h due to the high reversibility of the Li2CO3 formation and decomposition. The successful application of a three-dimensional self-supporting Cu@NCNF/CP cathode catalyst in Li-CO2 battery systems introduces a novel concept for developing high-performance transition metal-based catalysts.

B-N Co-Doped Biphenylene as a Metal-Free Cathode Catalyst for Li-O2 Batteries: a Computational Study.

Lithium-oxygen batteries (LOBs) meet the growing demand for long-distance transportation over electric vehicles but face challenges because of the lack of high-performance cathode catalysts. Herein, using density functional theory calculations, we report a unique graphene allotrope, biphenylene, of which the doping structures exhibit great potential as metal-free catalysts for LOBs. Our modeling results demonstrate that the biphenylene nanosheets retain metallic properties after B doping, N doping, or B-N co-doping. Compared with the pristine biphenylene, the catalytic activity of the doped biphenylene is greatly improved due to charge redistributions. Notably, the overpotentials of the B-N co-doped biphenylene are as low as 0.19 and 0.18 V for the discharge and charge processes, respectively. Based on the electronic structure and bonding analysis, we identify two factors, i. e., Li-O bond strength and *Li2 O2 adsorption energy, that can influence the Li-O2 electrochemical reactions. This study not only proposes a promising cathode catalyst but also provides insights into optimizing cathode catalysts for LOBs.

Temperature-dependent oxygen reduction activity of NiO thin film

The temperature-dependence activity of nickel oxide (NiO) thin films for the oxygen reduction reaction (ORR) in 1 M KOH was investigated using sol–gel and spin coating techniques. The peak current density for the ORR was evaluated between room temperature and 100 °C, showing an increase with temperature. XRD and SEM confirmed the formation of cubic phase NiO and uniform morphology of the thin film, respectively. Cyclic voltammetry was used to evaluate the electrocatalytic performance of the NiO film and its temperature sensitivity. The increased activity was attributed to the increased apparent activation energy of the ORR, which also reflected the semiconducting properties of NiO thin film. The findings provide valuable insights into the electrocatalysis of ORR on NiO, which has potential applications in the development of high-performance cathode catalyst.

High-Performance Zn-I2 Batteries Enabled by a Metal-Free Defect-Rich Carbon Cathode Catalyst.

Aqueous iodine-zinc (Zn-I2) batteries based on I2 conversion reaction are one of the promising energy storage devices due to their high safety, low-cost zinc metal anode, and abundant I2 sources. However, the performance of Zn-I2 batteries is limited by the sluggish I2 conversion reaction kinetics, leading to poor rate capability and cycle performance. Herein, we develop a defect-rich carbon as a high-performance cathode catalyst for I2 loading and conversion, which exhibits excellent iodine reduction reaction (IRR) activity with a high reduction potential of 1.248 V (vs Zn/Zn2+) and a high peak current density of 20.74 mA cm-2, superior to a nitrogen-doped carbon. The I2-loaded defect-rich carbon (DG1100/I2) cathode achieves a large specific capacity of 261.4 mA h g-1 at 1.0 A g-1, a high rate capability of 131.9 mA h g-1 at 10 A g-1, and long-term stability with a high retention of 88.1% over 3500 cycles. Density functional theory calculations indicated that the carbon seven-membered ring (C7) defect site possesses the lowest adsorption energies for iodine species among several defect sites, which contributes to the high catalytic activity for IRR and the corresponding electrochemical performance of Zn-I2 batteries. This work offers a defect engineering strategy for boosting the performance of Zn-I2 batteries.

Inducing Covalent Atomic Interaction in Intermetallic Pt Alloy Nanocatalysts for High-Performance Fuel Cells.

The harsh working environments of proton exchange membrane fuel cells (PEMFCs) pose huge challenges to the stability of Pt-based alloy catalysts. The widespread presence of metallic bonds with significantly delocalized electron distribution often lead to component segregation and rapid performance decay. Here we report L10 -Pt2 CuGa intermetallic nanoparticles with a unique covalent atomic interaction between Pt-Ga as high-performance PEMFC cathode catalysts. The L10 -Pt2 CuGa/C catalyst shows superb oxygen reduction reaction (ORR) activity and stability in fuel cell cathode (mass activity=0.57 A mgPt -1 at 0.9 V, peak power density=2.60/1.24 W cm-2 in H2 -O2 /air, 28 mV voltage loss at 0.8 A cm-2 after 30 000 cycles). Theoretical calculations reveal the optimized adsorption of oxygen intermediates via the formed biaxial strain on L10 -Pt2 CuGa surface, and the durability enhancement stems from the stronger Pt-M bonds than those in L11 -PtCu resulted from Pt-Ga covalent interactions.

Self-template synthesis of Fe–Nx doped porous carbon as efficient oxygen reduction reaction catalysts in zinc air batteries

Metal-nitrogen doped carbon materials (M/NCs) exhibit considerable potential as electrocatalysts for oxygen reduction reaction (ORR) in novel energy conversion and storage devices. Herein, the Fe–Nx doped porous carbon catalysts (FeNxPCs) with three-dimensional (3D) pore structure are synthesized by in situ pyrolyzation of polypyrrole-coated Fe2O3 (Fe2O3@PPy). Fe2O3 derived from the iron-formate framework (Fe-FF) is partially dissolved to generate Fe3+ for driving polymerization and served as template to form the 3D structure during polymerization. FeNxPCs exhibit satisfactory long-term durability and superior ORR activity (E1/2 = 0.89 V) compared to commercial Pt/C. The Zn-air battery (ZAB) assembled with FeNxPCs reveals excellent battery performance, including a high open circuit voltage of 1.50 V, peak power density of 155.4 mW cm−2, and cycling stability with 500 cycles. The excellent ORR activity of FeNxPCs could be ascribed to the porous structure, Fe–Nx active sites, and high defect level of FeNxPCs. This strategy can modulate 3D porous structure via self-template synthesis, which provides a novel insight for development of high-performance air cathode catalyst.

Candle Soot Nanoparticles versus Multiwalled Carbon Nanotubes as a High-Performance Cathode Catalyst for Li–CO2Mars Batteries for Mars Exploration

Increased CO2 emissions on the earth causing global warming and climate change have provided a thrust to explore Li–CO2 battery chemistry, where CO2 is used as an energy carrier. In addition, the occurrence of CO2 as a major natural abundant gas in the Martian atmosphere opens the possibility of using Li–CO2 batteries for interplanetary Mars missions. In this work, we aim to investigate facile and inexpensive candle soot carbon nanoparticles as a cathode catalyst against commercially available multiwalled carbon nanotubes (MWCNTs) for stable and high-performance Li–CO2 batteries for Mars exploration. The unique interconnected morphology and higher surface area of candle soot nanoparticles facilitate better reversibility (more than 80 cycles) compared to MWCNTs even at a high current density of 200 mA g–1 with a cutoff capacity of 500 mAh g–1. The full discharge capacity for candle soot nanoparticles was measured to be 5318 mAh g–1 with a coulombic efficiency of 42% as compared to 16% for MWCNTs. The rate capability studies were performed to establish the ability to operate the system reversibly at different current densities in a simulated Martian atmosphere. The outcome of this study paves the way toward developing a candle soot cathode-based practicable Li–CO2 battery for utilization on Mars.

Engineering the electronic structure of high performance FeCo bimetallic cathode catalysts for microbial fuel cell application in treating wastewater

The development of high-performance, strong-durability and low-cost cathode catalysts toward oxygen reduction reaction (ORR) is of great significance for microbial fuel cells (MFCs). In this study, a series of bimetallic catalysts were synthesized by pyrolyzing a mixture of g-C3N4 and Fe, Co-tannic complex with various Fe/Co atomic ratios. The initial Fe/Co atomic ratio (3.5:0.5, 3:1, 2:2, 1:3) could regulate the electronic state, which effectively promoted the intrinsic electrocatalytic ORR activity. The alloy metal particles and metal-Nx sites presented on the catalyst surface. In addition, N-doped carbon interconnected network consisting of graphene-like and bamboo-like carbon nanotube structure derived from g-C3N4 provided more accessible active sites. The resultant Fe3Co1 catalyst calcined at 700 °C (Fe3Co1-700) exhibited high catalytic performance in neutral electrolyte with a half-wave potential of 0.661 V, exceeding that of the commercial Pt/C (0.6 V). As expected, the single chamber microbial fuel cell (SCMFC) with 1 mg/cm2 loading of Fe3Co1-700 catalyst as the cathode catalyst afforded a maximum power density of 1425 mW/m2, which was 10.5% higher than commercial Pt/C catalyst with the same loading (1290 mW/m2) and comparable to the Pt/C catalyst with 2.5 times higher loading ( 1430 mW/m2). Additionally, the Fe3Co1-700 also displayed better long-term stability over 1100 h than the Pt/C. This work provides an effective strategy for regulating the surface electronic state in the bimetallic electro-catalyst.

Nanofibrous Cathode Catalysts with MoC Nanoparticles Embedded in N-Rich Carbon Shells for Low-Overpotential Li–CO2 Batteries

Li-CO2 batteries with high theoretical energy densities are recognized as next-generation energy storage devices for addressing the range anxiety and environmental issues encountered in the field of electric transportation. However, cathode catalysts with unsatisfactory activity toward CO2 absorption and reduction/evolution reactions hinder the development of Li-CO2 batteries with desired specific capacities and sufficient cycle numbers. In this work, a multifunctional nanofibrous cathode catalyst that integrates N-rich carbon shells embedded with molybdenum carbide nanoparticles and multiwalled carbon nanotube cores was designed and prepared. The N-rich carbon shell could strengthen the absorption capacity of CO2 and Li2CO3. The molybdenum carbide nanoparticles would improve the catalytic activity of both CO2 reduction and evolution reactions. The carbon nanotube cores would provide an efficient network for electron transportation. The synergistic effect of the cathode catalysts enhances the electrochemical performance of Li-CO2 batteries. A high cycling stability of more than 150 cycles at a current density of 250 mA g-1 with a cutoff capacity of 1000 mAh g-1 and a charge/discharge overpotential of less than 1.5 V is achieved. This work provides a feasible strategy for the design of a high-performance cathode catalyst for lithium-air batteries.

Surface strain-enhanced MoS2 as a high-performance cathode catalyst for lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) are one of the main candidates for the next generation of energy storage systems. To improve the performance of LSBs, we herein propose the use of strained MoS2 (s-MoS2) as a catalytically active sulfur host. The introduction of strain in the MoS2 surface, which alters its atomic positions and expands the S–Mo–S angle, shifts the d-band center closer to the Fermi level and provides the surface with abundant and highly active catalytic sites; these enhance the catalyst's ability to adsorb lithium polysulfides (LiPS), accelerating its catalytic conversion and promoting lithium-ion transferability. Strain is generated through the synthesis of core–shell nanoparticles, using different metal sulfides as strain-inducing cores. s-MoS2 nanoparticles are supported on carbon nanofibers (CNF/s-MoS2), and the resulting electrodes are characterized by capacities of 1290 and 657 ​mAh g−1 ​at 0.2 and 5 ​C, respectively, with a 0.05% capacity decay rate per cycle at 8 ​C during 700 cycles. Overall, this work not only provides an ingenious and effective strategy to regulate LiPS adsorption and conversion through strain engineering, but also indicates a path toward the application of strain engineering in other energy storage and conversion fields.

Strained Pt(221) Facet in a PtCo@Pt-Rich Catalyst Boosts Oxygen Reduction and Hydrogen Evolution Activity

Over the last years, the development of highly active and durable Pt-based electrocatalysts has been identified as the main target for a large-scale industrial application of fuel cells. In this work, we make a significant step ahead in this direction by preparing a high-performance electrocatalyst and suggesting new structure-activity design concepts which could shape the future of oxygen reduction reaction (ORR) catalyst design. For this, we present a new one-dimensional nanowire catalyst consisting of a L10 ordered intermetallic PtCo alloy core and compressively strained high-index facets in the Pt-rich shell. We find the nanoscale PtCo catalyst to provide an excellent turnover for the ORR and hydrogen evolution reaction (HER), which we explain from high-resolution transmission electron microscopy and density functional theory calculations to be due to the high ratio of Pt(221) facets. These facets include highly active ORR and HER sites surprisingly on the terraces which are activated by a combination of sub-surface Co-induced high Miller index-related strain and oxygen coverage on the step sites. The low dimensionality of the catalyst provides a cost-efficient use of Pt. In addition, the high catalytic activity and durability are found during both half-cell and proton exchange membrane fuel cell (PEMFC) operations for both ORR and HER. We believe the revealed design concepts for generating active sites on the Pt-based catalyst can open up a new pathway toward the development of high-performance cathode catalysts for PEMFCs and other catalytic systems.

Review on bimetallic catalysts for electrocatalytic denitrification

Accelerated industrialization disrupts the global nitrogen cycle, resulting in alarmingly increased nitrate in groundwater and other water bodies. Electrocatalytic nitrate reduction (NO3RR) with high automation can effectively remove nitrate from polluted water, thus avoiding nitrate accumulation. However, the sluggish cathode reaction kinetics severely hampered the efficiency of NO3RR. Developing high-performance cathode catalysts is of great significance for boosting NO3RR. Compared with pure metal catalysts, bimetal catalysts can further improve the cathode activity and selectivity to nitrogen or ammonia in the electrocatalytic process, attracting extensive research interest. In this review, we discussed the background of denitrification requirements and the development status of bimetallic denitrification catalyst. Metallic cathode catalysts, such as noble-metal, 3d transition metal, main group metal, are described emphatically. Finally, present challenges and future outlook on bimetallic denitrification catalysts are depicted.

Super-assembled atomic Ir catalysts on Te substrates with synergistic catalytic capability for Li-CO2 batteries

Rechargeable Li-CO2 batteries (LCBs) are considered as a promising candidate for the next generation energy storage system, but still be impeded by the lack of high-performance cathode catalyst and poor understanding for the complicated reaction mechanism. In the present work, we demonstrate that the catalytic capability of cathode catalyst of LCBs can be remarkably enhanced from the accelerated reaction kinetics using a p-type substrate as adsorption/desorption promoter for refined reaction route. A carbon-free atomic Ir-Te cathode catalyst with Ir atomic cluster is uniformly super-assembled on the surface of Te nanowires forming an amorphous surface layer (ca. 3 nm) to maximize the catalytic capability of active Ir sites and provide a refined reaction pathway due to synergistic effect of Ir active sites and Te substrate. The adsorption ability of Li2C2O4 during discharging and the desorption ability of CO2 species during charging of the p-type Te substrate could both promote the catalytic reaction kinetics and optimize the reaction pathways on Ir active sites. Finally, a large specific capacity of 13,247.1 mAh g−1 and an excellent high rate cyclability with stably over 350 and 200 cycles at the current density of 1000 and 2000 mA g−1 are achieved. This contribution provides a rational design strategy for high performance cathode catalyst, and intrinsic insight towards the understanding the reaction mechanisms of LCBs.

Two-dimensional Mo-based compounds for the Li-O2 batteries: Catalytic performance and electronic structure studies

Rechargeable Li-O2 batteries have captured increasing attention owing to their ultra-high theoretical specific energy. However, this promising system is confronted with the large overpotential, limited discharge capacity and low cyclic life. Herein, three two-dimensional (2D) molybdenum-based compounds of MoN, MoO3 and MoS2 are used as cathode catalysts in Li-O2 batteries. The catalytic performance and electronic structures of these catalysts are compared comprehensively. Electrochemical test results reveal the superior battery performance of MoN cathodes, which deliver the highest specific discharge capacity of approximately 7400 mAh g−1 and the lowest discharge/charge overpotential of 0.19/0.72 V. Density functional theory (DFT) calculations demonstrate the metallic property of MoN whereas MoO3 and MoS2 are poor conductive. Besides, interface properties between MoN and Li2O2 products as well as reaction pathways of the Li-O2 battery with MoN cathode are also investigated detailedly by DFT calculations, explaining the excellent catalytic properties of MoN at the atomic level. The present work provides intrinsic insights into designing high-performance cathode catalysts for Li-O2 batteries with fine-tuned morphology and electronic characteristics.

Transition metal (Fe, Co, Ni) and sulfur codoped nitrogen-enriched hydrothermal carbon as high-performance cathode catalyst for microbial fuel cell

Microbial fuel cell (MFC), a new technology, uses microorganisms to decompose and oxidize the organic matter for bioelectricity generation. However, the sluggish oxygen reduction reaction of cathode catalyst is an important factor that affects electricity generation. Herein, nitrogen-enriched hydrothermal carbon doped with transition metal and sulfur heteroatoms was prepared. Carbon doped with iron, cobalt and nickel metal particles and nitrogen and sulfur heteroatoms (Fe-NSC, Co-NSC, Ni-NSC) exhibited maximum power densities of 2068 ± 32 mW m−2, 1736 ± 49 mW m−2 and 1441 ± 45 mW m−2, respectively. By analyzing the content and bonding configuration of nitrogen, sulfur, iron, cobalt and nickel, it is further verified that pyridinic nitrogen and graphitic nitrogen can reduce the charge transfer resistance, and iron–nitrogen (Fe–N) bonding and cobalt–nitrogen (Co–N) bonding are considered to be active sites which are beneficial to enhance oxygen reduction activity, while nickel–nitrogen (Ni–N) bonding is insensitive to oxygen reduction activity. Consequently, Fe-NSC is an effective catalyst for oxygen reduction reaction in MFC.

Porous polyetherimide separators controlled in‐situ by tetrabutyl titanate as polymer electrolyte with ionic liquid for lithium‐oxygen batteries

Due to its advantages in specific capacity, lithium-oxygen batteries are expected to increase the recharge mileage of electric vehicles. However, the safety and cycle stability problems of lithium-oxygen batteries have not been completely resolved. Herein, through the non-solvent-induced phase separation method combined with the in-situ hydrolysis modification strategy of tetrabutyl titanate, a type of polyetherimide (PEI) separator with typical finger-shaped pores and honeycomb-shaped supporting layer pore structure was prepared. After being infiltrated by EMIM-BF4 ionic liquid electrolyte, the ionic conductivity of the separator can reach 0.75 mS cm−1. Due to the low crystallinity, high thermal stability, and stable ion transport pore structure of the separators, the assembled lithium-oxygen batteries can stably cycle for more than 75 cycles under the condition of a limit of 1000 mAh g−1. In addition, under the strategy of high-performance cathode catalysts and electrolyte additives, the application of the porous PEI separators in lithium-oxygen batteries will be further expanded.

Zn-doped CaFeO3 perovskite-derived high performed catalyst on oxygen reduction reaction in microbial fuel cells

Stable perovskite oxide is considered as a potential cathode for microbial fuel cells (MFCs). Herein, Zn is used as an effective element to modify the micro-structure and oxygen vacancy of perovskite to be a novel cathode catalyst. Physical characterizations show that due to partial volatilization at high temperature of Zn, perovskite forms hierarchically porous structures. Moreover, Zn is precipitated in electrochemical reaction to generate Zn vacancy in situ; thus, the active center of Fe has a superior interaction with oxygen-containing species, promoting the production of oxygen vacancy and forms a mixed valence state of Fe2+/Fe3+. The Zn-doped perovskite material CaFe0·7Zn0·3O3 exhibits remarkable oxygen reduction reaction (ORR) performances with outstanding onset potential (0.194 V vs. Ag/AgCl) and half-wave potential (−0.219 V vs. Ag/AgCl) under alkaline condition, which is better than Pt/C catalyst. Besides, CaFe0·7Zn0·3O3 shows an excellent four-electron pathway of ORR mechanism with remarkable corrosion resistance and stability, which enables a more reliable cathode electrocatalyst. The maximum power density of CaFe0·7Zn0·3O3 (892.10 ± 90.79 mW m−3) testing on microbial fuel cell is comparable to the maximum power density (1012.86 ± 84.03 mW m−3) of Pt/C. The findings of this work provide the feasibility of exploring inexpensive and high-performance cathode catalyst.

Single-side functionalized graphene as promising cathode catalysts in nonaqueous lithium-oxygen batteries.

High-performance cathode catalysts are always desirable for nonaqueous lithium-oxygen (Li-O2) batteries. Using density functional theory calculations, the structural, electronic, and magnetic properties of SSX-Gr with different C/X ratios (X = H or F) are systematically studied. Then, a detailed mechanism on the dissociation of O2 and the migration of Li on the SSX-Gr is revealed, based on which C6X and C8X are confirmed as the potential candidates as cathode catalysts. The studies on reaction pathways suggest that the four-electron pathway is the more possible catalytic pathway for the selected SSX-Gr. The free energy diagrams for discharging and charging processes catalyzed by SSX-Gr reveal that C6F exhibits the highest application potential due to its considerably low oxygen reduction overpotential (0.83 V) and oxygen evolution overpotential (1.47 V). The extra spins induced by single-side functionalization endow graphene with the electrocatalytic activity.