Active Cathode Research Articles

Heterogeneous Catalyst Coating for Boosting the Activity and Chromium Tolerance of Cathodes for Solid Oxide Fuel Cells

AbstractA challenge hindering the development of durable solid oxide fuel cells (SOFCs) is the significant performance degradation of cathodes owing to poisoning by volatile Cr originating from the Fe─Cr alloy interconnect. Herein, a heterogeneous catalyst coating, composed of Ba1−xCe0.8Gd0.2O3–δ and BaCO3, remarkably improves the oxygen adsorption, dissociation capability, and Cr resistance of a La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) cathode is demonstrated. The coherent heterointerface interactions formed between the catalyst coating and LSCF result in varied levels of surface strain and electrostatic interactions, significantly suppressing Sr surface segregation on LSCF. A single cell with the catalyst coating‐decorated LSCF (CC‐LSCF) achieves a peak power density of 1.73 W cm−2 at 750 °C, with no noticeable performance degradation for 100 h. The CC‐LSCF cathode also exhibits outstanding durability under accelerated Cr poisoning conditions, compared with the tremendous degradation rate of 0.42% h−1 for the bare LSCF cathode. The enhanced Cr resistance is attributed to synergy induced by the stabilization of the lattice Sr cations by heterointerface interactions and the remarkable structural stability of the catalyst coating under Cr poisoning conditions. The novel heterointerface engineering strategy in this study provides insight into the design and development of active and Cr‐tolerant cathodes.

Assessing the Performance of Continuous-Flow Microbial Fuel Cells and Membrane Electrode Assembly with Electrodeposited Mn Oxide Catalyst

Microbial fuel cells (MFCs) are considered promising energy sources whereby chemical energy is converted into electricity via bioelectrochemical reactions utilizing microorganisms. Several factors affect MFC performance, including cathodic reduction of oxygen, electrode materials, cell internal and external resistances, and cell design. This work describes the effect of the catalyst coating in the air-cathode membrane electrode assembly (MEA) for a microbial fuel cell (MFC) prepared via electrodeposition of manganese oxide. The characterization of the synthesized air-cathode MFC, operating in a continuous mode, was made via electrochemical impedance spectroscopy (EIS) analyses for the determination of the intrinsic properties of the electrode that are crucial for scalability purposes. EIS analysis of the MFCs and of the MEA reveals that the anode and cathode contribute to polarization resistance by about 85% and 15%, respectively, confirming the high catalytic activity of the Mn-based air cathode. The maximum power density of the Mn-based cathode is about 20% higher than that recorded using a Pt/C electrode.

Quantifying cathode biofilm resistance in a cdrAB modified Shewanella oneidensis MR-1 using electrochemical impedance spectroscopy

A range of biotechnological applications for converting electricity to fixed metabolic substrates is fuelling the study of cathodic bioelectrochemical systems. Shewanella oneidensis MR-1 has emerged as an important model system for extracellular electron uptake on cathodes, as many of the proteins involved in this process overlap with the organism's previously characterized extracellular electron transport machinery. However, there are still many questions surrounding the mechanics of electron uptake in Shewanella stemming largely from the challenge of quantifying biomass on electrode surfaces. This limits our understanding of the physiologic and kinetic constraints of electron uptake, as well as our ability to make meaningful comparisons across systems. To investigate the relationship between cathodic activity and biomass, we used a Shewanella oneidensis strain genetically modified with cell aggregation protein CdrAB behind a blue light-controlled promotor. Using blue light exposure to control cell deposition, we then investigated the relationship between cathodic activity and biomass. Electrochemical impedance spectroscopy (EIS) confirmed a decrease in biofilm impedance over a range of blue light exposures (i.e., 2 to 8 h). Consistent with previous results, after this timepoint, a drop-in electrochemical activity was observed, and impedances increased. For biofilms within the 2–8 h light exposure range, we observed a trend towards increased biological current consumption by quantifying the difference between pre and post kill currents. Comparing EIS data between pre and post kill experiments supported an increase in impedance post addition of killing agents and a trend towards the lowest biofilm impedances observed in the longest blue light exposed systems. Using an equivalent circuit model to extrapolate specific biofilm parameters we quantified the charger transfer resistance within the biofilm that corresponds to varying biofilm thicknesses and matches previously observed activities. For example, electrochemical activity was highest for the 8 h blue light exposed biofilm condition, with a maximum cathodic biologic current of -5.49 ± 0.85 µA, and a biofilm charge transfer resistance measured at 6909.5 ± 2136.5 Ω. On an individual reactor basis, we correlate this biofilm charge transfer resistance with biologic cathodic current. We observed a linear trend with a correlation score of 0.87 (r2 = 0.773). To the best of our knowledge, this is the first investigation of biofilm physiology on Shewanella cathodes using EIS. Continued efforts in this direction will further our understanding of biofilm-electrode interface during extracellular electron uptake with the goal of enhancing applications to bioelectrochemical systems.

Optimizing Interplanar Spacing, Oxygen Vacancies and Micromorphology via Lithium-Ion Pre-Insertion into Ammonium Vanadate Nanosheets for Advanced Cathodes in Aqueous Zinc-Ion Batteries.

Ammonium vanadates, featuring an N─H···O hydrogen bond network structure between NH4 + and V─O layers, have become popular cathode materials for aqueous zinc-ion batteries (AZIBs). Their appeal lies in their multi-electron transfer, high specific capacity, and facile synthesis. However, a major drawback arises as Zn2+ ions tend to form bonds with electronegative oxygen atoms between V─O layers during cycling, leading to irreversible structural collapse. Herein, Li+ pre-insertion into the intermediate layer of NH4V4O10 is proposed to enhance the electrochemical activity of ammonium vanadate cathodes for AZIBs, which extends the interlayer distance of NH4V4O10 to 9.8Å and offers large interlaminar channels for Zn2+ (de)intercalation. Moreover, Li+ intercalation weakens the crystallinity, transforms the micromorphology from non-nanostructured strips to ultrathin nanosheets, and increases the level of oxygen defects, thus exposing more active sites for ion and electron transport, facilitating electrolyte penetration, and improving electrochemical kinetics of electrode. In addition, the introduction of Li+ significantly reduces the bandgap by 0.18eV, enhancing electron transfer in redox reactions. Leveraging these unique advantages, the Li+ pre-intercalated NH4V4O10 cathode exhibits a high reversible capacity of 486.1mAhg-1 at 0.5Ag-1 and an impressive capacity retention rate of 72% after 5,000 cycles at 5Ag-1.

Modulating the oxygen redox activity of an ultra-high capacity P3 type cathode for sodium-ion batteries via beryllium introduced

Sodium-ion batteries (SIBs) show great potential for energy storage due to their good electrochemical properties and intrinsic cost performance, and sodium-ion cathode materials with high capacity and stable structure are the inevitable future development trend. While conventional anionic redox-active layered oxide cathode materials offer the advantage of extra capacity, challenges such as irreversible oxygen release still need to be addressed. Herein, beryllium is successfully introduced into P3-NaxLiyMn1-yO2 series of layered oxide materials for the first time, and the developed P3-Na0.6Li0.2Be0.25Mn0.675O2 (NLBMO) with the modulation of lattice oxygen activity can reach an ultra-high reversible capacity of 212.6 mAh g−1, significantly surpassing the P3-Na0.6Li0.2Mn0.8O2 (NLMO, 165.7 mAh g−1). Based on a comprehensive comparison with the P3-NLMO, the effect of beryllium on the Mn/O charge complementary mechanism is revealed. Since the strong covalency of beryllium can inhibit the oxidation of excess O through the formation of stable Be-O bonds, while irreversible peroxidation of partially unstable (O2)n− occurs to stimulate more Mn4+/Mn3+ to replace O for charge compensation. As a result, pollution and structural damage caused by O peroxidation are effectively suppressed while achieving ultra-high capacity. In-situ XRD reveals that P3-NLBMO exhibits high structural reversibility during charging and discharging processes, indicating that the formation of Be-O bonds can also further stabilize the crystal structure during cycling. Therefore, beryllium modification strategy proposed in this work provides a novel route to synthesize novel SIBs cathode materials with higher performance.

Grain-refining Co0.85Se@CNT cathode catalyst with promoted Li2O2 growth kinetics for lithium-oxygen batteries

Highly active cathode catalysts for efficient formation/decomposition of Li2O2 are essential for the performance improvement of lithium-oxygen batteries (LOBs). In this study, a grain-refining Co0.85Se catalyst with a lattice spacing of 2.69 Å of (101) plane closely matching with the (100) plane (2.72 Å) of Li2O2 was applied for high-performance LOBs. Highly (101) plane exposed Co0.85Se@CNT was synthesized by a simple one-pot hydrothermal method. The Co0.85Se with the lattice matching effect not only led to the efficient conversion and polarized growth of Li2O2, but also prevented the formation of byproducts. Density functional theory (DFT) calculations reveal that Co0.85Se (101) plane has the intrinsic catalytic ability to generate/decompose Li2O2 during ORR/OER process, due to its homogeneous electron distribution, suitable adsorption energy, and promoted Li2O2 growth kinetics. As a consequence, the (101) plane highly exposed Co0.85Se@CNT-80 electrode exhibited remarkable cycle stability over 2400 h at 100 mA/g and 290 cycles at 500 mA/g, which is about 2 times longer than other electrodes.

Bias distribution and regulation in photoelectrochemical overall water-splitting cells.

The water oxidation half-reaction at anodes is always considered the rate-limiting step of overall water splitting (OWS), but the actual bias distribution between photoanodes and cathodes of photoelectrochemical (PEC) OWS cells has not been investigated systematically. In this work, we find that, for PEC cells consisting of photoanodes (nickel-modified n-Si [Ni/n-Si] and α-Fe2O3) with low photovoltage (Vph < 1V), a large portion of applied bias is exerted on the Pt cathode for satisfying the hydrogen evolution thermodynamics, showing a thermodynamics-controlled characteristic. In contrast, for photoanodes (TiO2 and BiVO4) with Vph > 1V, the bias required for cathode activation can be significantly reduced, exhibiting a kinetics-controlled characteristic. Further investigations show that the bias distribution can be regulated by tuning the electrolyte pH and using alternative half-reaction couplings. Accordingly, a volcano plot is presented for the rational design of the overall reactions and unbiased PEC cells. Motivated by this, an unbiased PEC cell consisting of a simple Ni/n-Si photoanode and Pt cathode is assembled, delivering a photocurrent density of 5.3±0.2mA cm-2.

Cobalt-Mediated Defect Engineering Endows High Reversible Amorphous VS4 Anode for Advanced Sodium-Ion Storage.

Metal sulfides are promising anode materials for sodium-ion batteries (SIBs) due to their structural diversity and high theoretical capacity, but the severe capacity decay and inferior rate capability caused by poor structural stability and sluggish kinetics impede their practical applications. Herein, a cobalt-doped amorphous VS4 wrapped by reduced graphene oxide (i.e., Co0.5-VS4/rGO) is developed through a Co-induced defect engineering strategy to boost the kinetics performances. The as-prepared Co0.5-VS4/rGO demonstrates excellent rate capacities over 10Ag-1 and superior cycling stability at 5Ag-1 over 1600 cycles, which is attributed to the defects formed by Co doping, the formed amorphous structure and the robust rGO substrate. The great features of Co0.5-VS4/rGO anode are further confirmed in sodium-ion capacitors when the active carbon cathode is used. Additionally, the relationships between metal doping, the derived defects, the amorphous structure, and the sodium storage of VS4 are uncovered. This work provides deep insights into preparing amorphous functional materials and also probes the potential applications of metal sulfide-based electrode materials for advanced batteries.

Ultrafast and Durable Sodium-Ion Storage of Pseudocapacitive VN@C Hybrid Nanorods from Metal-Organic Framework.

Vanadium nitride (VN) is a promising electrode material for sodium-ion storage due to its multivalent states and high electrical conductivity. However, its electrochemical performance has not been fully explored and the storage mechanism remains to be clarified up to date. Here, the possibility of VN/carbon hybrid nanorods synthesized from a metal-organic framework for ultrafast and durable sodium-ion storage is demonstrated. The VN/carbon electrode delivers a high specific capacity (352mA h g-1), fast-charging capability (within 47.5 s), and ultralong cycling stability (10000 cycles) for sodium-ion storage. In situ XRD characterization and density functional theory (DFT) calculations reveal that surface-redox reactions at vanadium sites are the dominant sodium-ion storage mechanism. An energy-power balanced hybrid capacitor device is verified by assembling the VN/carbon anode and active carbon cathode, and it shows a maximum energy density of 103Wh kg-1 at a power density of 113W kg-1.

Electrochemical activity of electroless Ni-P coatings in the hydrogen evolution reaction

The purpose of this study was investigation of the electrochemical activity of Ni-P coatings, differing in phosphorus content and structure, in the hydrogen evolution reaction (HER) and the identification of the reasons for their high activity in the reaction being studied. The coatings were deposited from an electroless nickel plating solution, the phosphorus content in the coatings (from 4.8 to 8.0 wt. %) varied by changing the pH of the solution. It was found that during cathodic polarization in 0.5 M H2SO4 additional surface activation occurs as a result of dissolution of the surface layer of the coating, removal of phosphorus from the surface layer, and development of the electrode surface. Of all the coatings studied coatings containing 4.8% phosphorus were most susceptible to cathodic activation. Coatings with a phosphorus content of 8.0% were least susceptible to cathodic activation. The similar electrochemical activity of the studied coatings (taking into account the roughness factor) in HER indicates that, as a result of cathodic polarization, the composition of the thin surface layer on which the cathodic reaction occurs is approximately the same, regardless of the initial phosphorus content

Electrochemical Activation of Fe-LiF Conversion Cathodes in Thin-Film Solid-State Batteries.

Transition metal fluoride (TMF) conversion-type cathodes promise up to 4 times higher gravimetric energy densities compared to those of common intercalation-type cathodes. However, TMF cathodes demonstrate sluggish kinetics, poor efficiencies, and incompatibility with many liquid electrolytes. In this work, coevaporated heterostructured iron and lithium fluoride (Fe-LiF) cathodes are investigated in thin-film solid-state batteries with a LiPON electrolyte and a lithium metal anode. The cells were cycled 2000 times at a cycling rate of 6C. They show a gradual improvement in voltaic efficiency (37-53%) and specific capacity (146-216 mAh/g) during cycling. After 2000 cycles, the cathode capacity reaches 480 mAh/g at a cycling rate of C/3.6, close to its theoretical capacity of 498 mAh/g, at room temperature conditions. This capacity gain is correlated with an observed electrochemically activated nanorestructuring of the cathode, characterized by cycling-induced coarsening (from 2.8 to 4.2 nm) of the metallic iron phase and its accumulation near the current collector interface, as well as lithium fluoride phase accumulation near the LiPON interface.

Balance the conductivity and enhance chemical stability of BaCe0.3Fe0.7O3–δ by tuning A-site cation deficiency

Triple-conducting perovskites are the focus of extensive research and have emerged as high-performance cathode materials for proton-conducting solid oxide fuel cells (H–SOFCs). Notably, BaCe0.36Fe0.64O3-δ (BCF36) has recently garnered attention for its ability to provide suitable oxygen ion conductivity and proton conductivity, all through skillful composition tuning. Here, A-site deficient BaCe0.3Fe0.7O3-δ (D-BCF30) is prepared to further boost the cathode activity. The composition content is modified by introducing Ba cation deficiency according to XRD and calculation results. Remarkably, the single cell equipped with D-BCF30 cathode demonstrates a significantly enhancement in performance, featuring a high power density of 1425 mW cm−2 and a low polarization resistance of 0.045 Ω cm2 at 700 °C compared to stoichiometric BCF30. Moreover, the cell operation durability has markedly improved which is further substantiated through experiments and density functional theory (DFT) calculations, suggesting a promising avenue to improve performance and stability of H–SOFCs.

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

Estimating the corrosion rate of stainless steel R-SUS304ULC in nitric acid media under concentrating operation

The amount of corrosion of the austenitic stainless steel was evaluated considering the changes in solution composition and boiling during actual concentration operations. Austenitic stainless steel R-SUS304ULC is the structural material of the highly radioactive liquid waste concentrator in Japanese spent fuel reprocessing plant, which treats highly corrosive nitric acid solutions during enrichment operations. The study results show that it is necessary to focus on nitric acid concentrations, oxidizing metal ion concentrations, and decompression boiling as factors that accelerate the corrosion rate of stainless steel because of cathodic reaction activation.

Effect of Cu2+ on deposition mechanism and structure of ZrO2-based conversion coatings on AA6060 aluminium alloys and their susceptibility to filiform corrosion

Zirconium oxide-based conversion coatings (CCs) were prepared from hexafluorozirconic acid, H2ZrF6, with and without CuII as an additive. The CCs were prepared on primary and recycled AA6060. The deposition mechanism, structure, electrochemical properties and effectiveness in protection against filiform corrosion (FFC) have been explored. In presence of CuII additives, a two step deposition mechanism is observed, evidenced by open circuit potential measurements and in situ dynamic electrochemical impedance spectroscopy. Copper deposits predominantly as copper(II) hydroxyfluoride on the top surface, and metallic Cu0 at the metal/CC interface, as evidenced by x-ray photoelectron spectroscopy and glow-discharge optical emission spectroscopy. The presence of a CuII additive induces a different distribution of the ZrO2-based products. After deposition of a weak organic model coating, aluminium pretreated with the CuII-containing system shows a 10%–30% lower maximum filament length compared to the CuII-free system in FFC tests, despite a ca. one order of magnitude higher cathodic activity of the former.

Tuning Redox Behavior of Sulfur Cathodes Via Ternary-Coordinated Single Fe Atom in Lithium-Sulfur Batteries.

Modulating the coordination configuration of single Fe atom has been an efficient strategy to strengthen the redox dynamics for lithium-sulfur batteries (LSBs) but remains challenging. Herein, the single Fe atom is functioned with nitrogen and carbon atoms in the first shell, and simultaneously, oxidized sulfur (─SOx) in the second shell, which presents a lower antibonding state and well address the redox activity of sulfur cathodes. In the ternary-coordinated single Fe atom catalyst (FeN2C2-SOx-NC), the binary structure of FeN2C2 provides a lower Fe-S bonding strength and d-p orbital hybridization, which obviously optimizes the adsorption and desorption behavior of sulfur species during the reduction and oxidation reaction processes. Simultaneously, the ─SOx redistributes the electron density of the coordinating nitrogen atoms, which possesses high electron-withdrawing ability and develops electrocatalytic activity. As a result, the sulfur cathodes with FeN2C2-SOx-NC present an excellent high-rate cyclic performance, accompanied by a capacity decay rate of 0.08% per cycle for 500 cycles at 4.0 C. This study provides new insights for optimizing the redox dynamics of sulfur cathodes in LSBs at the atomic level.

Vibrationally-resolved RIXS reveals OH-group formation in oxygen redox active Li-ion battery cathodes.

Vibrationally-resolved resonant inelastic X-ray scattering (VR-RIXS) at the O K-edge is emerging as a powerful tool for identifying embedded molecules in lithium-ion battery cathodes. Here, we investigate two known oxygen redox-active cathode materials: the commercial LixNi0.90Co0.05Al0.05O2 (NCA) used in electric vehicles and the high-capacity cathode material Li1.2Ni0.13Co0.13Mn0.54O2 (LRNMC) for next-generation Li-ion batteries. We report the detection of a novel vibrational RIXS signature for Li-ion battery cathodes appearing in the O K pre-peak above 533 eV that we attribute to OH-groups. We discuss likely locations and pathways for OH-group formation and accumulation throughout the active cathode material. Initial-cycle behaviour for LRNMC shows that OH-signal strength correlates with the cathodes state of charge, though reversibility is incomplete. The OH-group RIXS signal strength in long-term cycled NCA is retained. Thus, VR-RIXS offers a path for gaining new insights to oxygen reactions in battery materials.

Enhanced catalytic activity and stability of SOFC electrodes through plasma-driven surface modification

Plasma-induced surface amorphization prevents Sr phase separation, boosting the catalytic activity and stability of SOFC cathode. This finding expands the application of amorphous features to practical electrodes, previously limited to model studies.

Crystallization and electrochemical properties of KxV2O5 nano-ribbons obtained via a solvothermal process as a promising cathode for PIBs.

In this research, a series of K+-intercalated quasi-1D vanadium-based nano-ribbons (KxV2O5 NRs) were synthesized via a facile solvothermal method. The solvation and reductive effects of vanadium oxide precursors (V2O5 powder) on the crystallization and growth of KxV2O5 NRs were studied. Besides, post-heat treatment was performed to improve the crystallinity of KxV2O5 NRs. These KxV2O5 NRs were adopted as active cathodes for potassium-ion batteries (PIBs), whose K+ storage properties were systematically evaluated using various electrochemical methods. The relationship among the morphology, crystallinity, working voltage window and electrochemical reversible K+ storage performance of KxV2O5 NRs was studied and established. Results reveal that KxV2O5-HG, which was prepared via a solvothermal reaction involving a solvation process (using H2O2) and a proper reducing condition (proper dose of glucose) with V2O5 powder as the raw material, would be more beneficial for the reversible storage of K+ when used as the cathode for PIBs compared to other contrast samples. In addition, the enhanced crystallinity and slightly broadened working voltage window of KxV2O5-HG could hinder its long-term cycling stability upon repeated K+ insertions/extractions.

Self-sufficient metal-air battery systems enabled by solid-ion conductive interphases.

Metal-air batteries including Li-air, Na-air, Al-air, and Zn-air, have received significant scientific and technological interest for at least the last three decades. The interest stems primarily from the fact that the electrochemically active material (O2) in the cathode can in principle be harvested from the surroundings. In practice, however, parasitic reactions with reactive components other than oxygen in dry air passivate the anode, limit cycling stability of air-sensitive (e.g., Li, Na, Al) and electrolyte-sensitive (e.g., Zn) anodes, in most cases obviating the energy-density benefits of harvesting O2 from ambient air. As a compromise, so-called metal-oxygen batteries in which pure O2 is used as the active cathode material have been extensively studied but are understood to be of little practical relevance because of the large infrastructure required to produce the pure O2 stream. Here, we report on the design of solid-ion conductive chemically inert metal interphases that simultaneously protect a metal anode from parasitic reactions with electrolyte components and which facilitate rapid interfacial ion transport. Interphases composed of indium (In) are reported to be of particular interest for protecting Li and Na anodes from passivation in air whereas interphases composed of Sn are shown to prevent chemical and electrochemical corrosion of Zn anodes in alkaline electrolytes. We report further that these protections enable so-called self-sufficient metal-air batteries capable of extended cycling stability in ambient air environments.