Metal–air batteries offer substantially higher theoretical energy density than Li-ion batteries, rendering them suitable for stationary storage and advanced mobility applications, including eVTOL aircraft. Aluminum–air (Al–air) batteries are especially promising due to the natural abundance of Al and a theoretical energy density of approximately 8.1 kWh kg⁻¹, along with a specific capacity of about 2.9 Ah g⁻¹ [1]. This study presents a novel, membrane-less, mechanically rechargeable Al–air flow battery that integrates enhanced electrolyte and gas management using a flow-engineered architecture. The shallow electrolyte channel ensures even electrolyte (KOH) distribution and mitigates local corrosion, while the forced-convection cathode enhances oxygen transport to the catalyst layer. In 5 cm² prototypes operated at 70 °C, this configuration achieves an unprecedented 1.72 W cm⁻² at 0.75 V with pure oxygen and about 0.67 W cm⁻² at 1.12 V with air (shown in Figure 1), indicating ultrahigh-power output, exceeding known values demonstrated in the literature by at least a factor of three [2]. A comprehensive investigation was conducted to determine how operating conditions and cathode architecture influence the performance of membrane-less Al–air flow battery. Systematic variations in electrolyte flow rate, cell temperature, oxidizer type (pure oxygen and air), and oxidizer flow rate were implemented to quantify their individual and combined effects on mass transport, reaction kinetics, and parasitic corrosion, as assessed by electrochemical impedance spectroscopy (EIS). Furthermore, multiple gas diffusion layers (GDLs) with varying thicknesses, pore structures, microporous layer (MPL) configurations, and PTFE loadings were examined to assess how cathode transport resistance and wettability affect power output under different operating conditions. The resulting dataset establishes performance scaling laws and GDL selection guidelines for high-power Al–air operation across a broad design space, demonstrating that the flow-engineered, membrane-less architecture sustains robust, air-breathing performance even under oxidizer-limited, low-flow, or high/low-temperature scenarios. References: [1] R. Mori, “Recent Developments for Aluminum–Air Batteries,” Electrochemical Energy Reviews , vol. 3, no. 2. Springer Science and Business Media B.V., pp. 344–369, 2020. doi: 10.1007/s41918-020-00065-4. [2] H. Wen, Z. Liu, J. Qiao, R. Chen, R. Zhao, J. Wu, G. Qiao, and J. Yang, “High energy efficiency and high power density aluminum-air flow battery,” Int J Energy Res , vol. 44, no. 9, pp. 7568–7579, Jul. 2020, doi: 10.1002/er.5485. Figure 1

The aim of this study is to examine the development and makeup of the Solid Electrolyte Interphase (SEI) and Cathode Electrolyte Interphase (CEI) in lithium-ion batteries during rapid charging. Using X-ray photoelectron spectroscopy (XPS) and depth profiling, we investigate the chemical modifications occurring on the electrode surfaces during the initial formation and subsequent fast charge-discharge cycles. Our research shows that the anode's SEI initially comprises a thin layer rich in ketones, which then transforms into a thicker layer dominated by carbonaceous compounds during rapid charging cycles. Following assembly, lithium fluoride (LiF) quickly becomes a key element of the SEI, and its presence continues to grow substantially during the formation cycle, remaining the primary component throughout subsequent cycles. Initially, the cathode forms a thin oxide layer rich in ketones, with no noticeable carbonaceous CEI. The CEI primarily comprises LiF, which experiences an increase during the formation cycle and retains a thin layer of carbon coating after the initial rapid discharge. These findings show how the interphase layers impact the performance and stability of lithium-ion batteries, especially during fast charging for electric vertical take-off and landing (eVTOL) vehicles.

Lithium-ion battery performance degrades over time due to complex aging mechanisms, including lithium inventory loss, structural changes in electrode materials, and increases in contact resistance. Understanding these processes is essential for improving battery performance and extending cycle life. This work presents a combined electrochemical impedance spectroscopy and distribution of relaxation times approach using a three-electrode configuration to investigate aging and state-of-charge (SOC)-dependent internal resistances in NMC811 & boxv;graphite Li-ion cells. By simultaneously probing the cathode, anode, and full-cell responses and deconvoluting overlapping impedance features using DRT, we identify distinct contributions from particle-particle resistance, SEI resistance, intercalation (charge-transfer) kinetics, and solid-state diffusion. Our results show that cathode processes dominate impedance growth at high SOC due to structural degradation and surface reconstruction, whereas anode contributions arise mainly at low SOC through increasing intercalation-kinetic limitations. SEI-related resistance stabilizes after the initial cycles, while contact resistance and diffusion impedances grow steadily with aging. These trends correlate closely with SEM, XRD, and Raman evidence of particle cracking, lattice strain, and structural disorder, establishing strong links between electrochemical signatures and physical degradation. Overall, this methodology provides a quantitative, component-resolved framework for diagnosing electrode-specific failure modes and guiding materials or interface-engineering strategies to enhance the lifetime of lithium-ion cells.

While moment-based boundary conditions have proven highly effective for Lattice Boltzmann Methods (LBM), their application has traditionally been restricted to Multiple-Relaxation-Time (MRT) collision models and grid-aligned geometries. This paper presents a systematic framework for constructing moment-derived boundary conditions for Single-Relaxation-Time (SRT) LBM, explicitly extended to handle coupled multiphysics on complex curved boundaries. In this approach, unknown boundary variables are determined by imposing constraints on the hydrodynamic moments, and the corresponding distribution functions are reconstructed from the adjusted macroscopic variables. The framework is systematically derived via Chapman–Enskog analysis, yielding explicit boundary rules for flat walls, corners, and curved surfaces. By coupling a macroscopic ghost-node reconstruction scheme with moment-based constraints, the proposed method overcomes the geometric limitations of standard staircase-like approximations. The method’s robustness is further validated against standard benchmarks, including natural convection in a square cavity and flow past a heated cylinder. Results indicate that while standard bounce-back schemes remain competitive for simple isothermal no-slip walls, the proposed ghost-node moment framework provides superior consistency and geometric fidelity for coupled thermo-fluid systems on curved boundaries.

Transition-metal-substituted magnetite nanoparticles are promising bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy conversion and storage technologies. Mn-substituted magnetite nanocatalysts (MnxFe3-xO4, 0 ≤ x ≤ 1) were synthesized via a facile one-step polyol method, yielding crystalline spinel nanocatalysts with controlled size (6.5-13 nm) and composition without post-synthesis annealing. Systematic variation of the Mn/Fe ratio reveals that Mn substitution modulates the electronic structure, surface chemistry, and electrocatalytic performance. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization demonstrate that optimal bifunctional activity occurs at x ≈ 0.4-0.6, where MnFe-04 and MnFe-06 achieve ORR half-wave potentials of 0.589 and 0.574 V vs. RHE, near-ideal four-electron selectivity (n ≈ 3.98-3.99, %HO2−), and lowest bifunctional gaps in the series (ΔE = 1.242 and 1.228 V).This work provides a scalable, one-step synthesis strategy for designing cost-effective, precious-metal-free bifunctional electrocatalysts, advancing their viability for next-generation renewable energy applications such as metal-air batteries, regenerative fuel cells, and water electrolyzers.

The transference number is a critical parameter in solid-state batteries, as it determines how efficiently Li + ions move through the electrolyte to reach the electrode interface. We measured the transference number using a symmetric coin cell.

Transition-metal-substituted magnetite nanocatalysts show promise as bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy conversion and storage technologies. Here, we describe a simple one-step polyol synthesis method for producing Mn-substituted magnetite (MnₓFe₃₋ₓO₄, 0 ≤ x ≤ 1) nanocatalysts with controlled size (7-10 nm), composition, and crystal structure. This polyol method is a versatile wet-chemistry route that enables simultaneous nucleation and growth of metal precursors at a moderate temperature (175 °C) in diethylene glycol, yielding crystalline spinel-phase nanoparticles without post-synthesis annealing.Systematic variation of the Mn/Fe ratio reveals that Mn substitution modulates the electronic structure, surface chemistry, and catalytic activity for both ORR and OER. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization demonstrate that optimal bifunctional activity occurs at x ≈ 0.4-0.6, where enhanced conductivity and favorable oxidation-state distribution facilitate electron-transfer kinetics. Particle size effects show that smaller nanoparticles (7.3-9.2 nm) exhibit superior mass-normalized activity due to increased surface area.This straightforward synthesis offers a method for creating cost-effective, precious-metal-free bifunctional electrocatalysts for renewable energy applications, such as metal-air batteries, regenerative fuel cells, and water electrolyzers.

In this study, a novel path-percolation algorithm is introduced to simulate inhomogeneous porous channels. Furthermore, a novel double-path-percolation model was developed to simulate porous channels with lower-tortuosity void paths for fluid transfer and solid paths for heat and electron transfer. Micro-computed tomographies of two actual gas diffusion layer materials used in polymer electrolyte fuel cells were digitized and used in diffusion simulations to provide morphology precisely. A single-phase fluid flow through the inhomogeneous porous channels was simulated using a two-dimensional lattice Boltzmann model, where the fluid flow codes were ported on Nvidia GPUs using CUDA. The effective diffusion equations as a function of effective porosity and tortuosity were developed for single- and double-path-percolation models, respectively, and tested using the micro-computed tomographies of the gas diffusion layers.

A segmented cell and PCB approach was used to demonstrate an advanced technique for measuring and understanding the electrochemical behavior of PEM water electrolyzers. By employing a semi-empirical model, discrete modes of overpotential and their spatial distributions were identified in an operating cell. Distributed area-specific resistance (DASR) measurements indicate that local dehydration of the polymer electrolyte membrane is the primary driver of increased polarization, behaving similarly to mass transport-limited currents at low flow rates due to ineffective gas-phase bubble removal. To improve quantification, the overall ohmic overpotential is divided into background (eta Ohm,b) and mass transport-coupled (eta Ohm,mt) components. Two types of anode diffusion media, a baseline PTL and a thin foil liquid/gas diffusion layer (LGDL), were examined. The results show significant variations in eta Ohm,b and also highlight that ineffective bubble removal leads to pronounced local dehydration. The effect of cell temperature on various overpotentials was also examined. Negligible differences in diffusion overpotential were observed when comparing PEWE performance using the PTL and LGDL, despite major differences in two-phase fluid transport within each diffusion media. This underscores the critical role of the catalyst layer's micro-porous structure in diffusion processes. The study highlights the complex nature and intricacies of mass transport limitations within PEWEs, providing critical insights for improving system efficiency and advancing sustainable hydrogen production. High resolution distributed measurements for both current density and area specific resistance have been presented.Analyzing the data with a semi-empirical zero-dimensional model helps to identify local overpotentials at both the global and local scale.Bubble accumulation and effective water transport is seen to affect diffusion as well as ohmic contributions to overpotentials .Overpotentials show significant spatial variations in their distribution.

Metal oxide is being researched as a potential replacement for the graphite anode in lithium-ion batteries. This material offers several advantages as an alternative anode for advanced rechargeable batteries, including higher theoretical capacity, superior discharge potential, affordability, natural availability, and safety characteristics [1]. Furthermore, when formed as nanoparticles, increased surface area enhances electrode activity and facilitates faster ion transport, which improves lithium mobility in lithium-ion batteries. However, the stability of the nanoparticles is considered a significant challenge. In this work, we present the synthesis conditions and characterization of stable spinel manganese oxide nanoparticles with various sizes and morphologies and high crystallinity [2]. We demonstrate that it is possible to control the size and shape of these nanocrystals under specific conditions by using the polyol process [3]. These nanomaterials were tested in half-cell configurations using lithium metal as the counter and reference electrodes. Figure 1 (a) presents the TEM images of Mn₃O₄ nanocrystals, which exhibit uniform particle sizes in the range of approximately 7–10 nm. A nanocomposite anode was fabricated by combining these Mn₃O₄ nanoparticles with graphite. Figure 1 (b) displays the first formation cycle of the composite anode, demonstrating enhanced specific capacity relative to conventional graphite which has specific capacity of 350 mAh/g, indicative of improved electrochemical performance. In this study, we are developing composite anode materials with varying weight percentages of metal oxides and different sizes and morphologies to enhance capacity, rate capability, and stability. References: He, S. Wu, N. Zhao, C. Shi, E. Liu, and J. Li, Carbon-encapsulated Fe 3 O 4 nanoparticles as a high-rate lithium ion battery anode material, ACS Nano, 2013, 7, 4459–4469. Rhadfi, J.-Y. Piquemal, L. Sicard, F. Herbst, E. Briot, M. Benedetti, and A. Atlamsani, Polyol-made Mn 3 O 4 nanocrystals as efficient Fenton-like catalysts, Appl. Catal. A, 2010, 386, 132–139. Rhadfi, L. Sicard, F. Testard, O. Taché, A. Atlamsani, E. Anxolabéhère-Mallart, Le Y. Du, L. Binet, and J.-Y. Piquemal, A comprehensive study of the mechanism of formation of polyol-made hausmannite nanoparticles: from molecular species to solid precipitation J. Phys. Chem. C, 2012, 116, 5516. Figure 1

Secondary microparticles are synthesized using a Mn1.5Ni0.5(OH)(2)CO3 precursor, which undergoes thermal decomposition and calcination, releasing CO2 and H2O gaseous species. In situ high-temperature phase elucidation confirms the least degree of disordered phase LiMn1.5Ni0.5O4 cathode without rock-salt impurity phase and having insignificant content of Mn3+ to stable Fd 3 m structure. Raman spectrum shows a band at 590 cm(-1) (F-2g((3))) without splitting, confirming spinel compound derived with disordered phase. Microscopic analyses reveal secondary microparticles and segregated primary nanoparticles having surface coating-conducting network architecture. Cyclic voltammograms of primary nanoparticles show well-resolved two redox peaks at 4.7 V compared to secondary microparticles, confirming superior kinetic reversibility for Ni2+ to Ni3+ and Ni3+ to Ni4+ redox process. At 20C discharge, segregated primary nanoparticles exhibit a discharge flat voltage profile at 4.3 V and deliver a high reversible capacity of 100 mAh g(-1) for the 12th cycle and 86 mAh g(-1) for the 1000th cycle, while secondary microparticles deliver 70 mAh g(-1) for 12th cycle and declined its cycle operation at 250th cycle with the capacity of < 5 mAh g(-1). Results confirm a strong potential for use as a highly durable, cobalt-free, high-voltage cathode capable of high-rate discharge in LIBs.

In this study, tin (Sn) nanoparticles are demonstrated to effectively catalyze the reduction of CO2 to formate in an alkaline medium. Catalytically active Sn-based nanoparticles, supported on carbon black (Sn/C) and highly conductive graphene nanosheets (Sn/GN), present a promising approach to mitigating atmospheric CO2 emissions when integrated with capture technologies. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were employed to evaluate the prepared catalysts in CO2-saturated 0.5 M KHCO3 using a three-electrode rotating disk electrode (RDE) configuration. The results revealed a significantly lower charge-transfer resistance for graphene-supported tin compared to carbon black-supported tin. The CO2 reduction to formate was further demonstrated in a full electrochemical cell setup resembling the architecture of a low-temperature polymer electrolyte fuel cell (PEFC) operating in an alkaline medium with an anion exchange membrane (AEM). Performance tests were conducted with both triple-serpentine and parallel flow field architectures, showing flow rate-dependent behavior. Additionally, an ex-situ RDE technique was utilized to detect and quantify formate production during CO2 reduction in the full-cell configuration. This work highlights the importance of catalyst support materials and flow field design in optimizing CO2 electroreduction systems.

Aluminum-air batteries (AABs) have been attracting increasing attention due to their high specific energy, relatively low cost, and scalability [1]. Moreover, high-performance AABs could enable critical applications such as electric vehicles including aerial travel and military applications [2]. Alleviating limitations in AABs must address multiple processes. Among them, adopting a zero-gap cell design – commonly used in proton exchange membrane (PEM) fuel cells and electrolyzers – may allow for significantly higher power densities, which are essential for high energy and power applications. Developing a zero-gap cell structure to improve battery performance requires thorough investigation of the principal components, i.e., electrodes, diffusion media, membranes/separators, electrolytes, and cell architecture. Especially for high-power applications, commercialization of AABs requires a thorough understanding of optimal cell conditions and architecture [3]. In this study, we investigated the effects of varying aluminum purities and oxidant quality on AAB performance. In our novel cell architecture, we demonstrate enhanced battery performance, achieving high power densities exceeding 1 W cm⁻² — an outcome not previously reported in the literature, to the best of our knowledge. Overall, this research provides valuable insights into the advancement of high-power AABs and their potential in critical applications. References Rani, B., et al., Aluminum–air batteries: current advances and promises with future directions. RSC Advances, 2024. 14 (25): p. 17628-17663. Dilshad, M., et al., Next-Generation Aluminum-Air Batteries: Integrating New Materials and Technologies for Superior Performance. ACS Applied Energy Materials, 2025. 8 (6): p. 3248-3275. Gaele, M. F. and T. M. Di Palma, Polymer Electrolytes for Al-Air Batteries: Current State and Future Perspectives. Energy & Fuels, 2022. 36 (21): p. 12875-12895. Figure 1

Mass transport processes play a significant role in the proton exchange membrane electrolyzer cells (PEMECs) to produce affordable “green hydrogen”. However, the strong interaction among components of PEMECs results in complex transport processes, involving multiple mass, phase, and scale, which is challenging to be experimentally probed. Herein, we developed a fully validated 3D multiphysics model to describe and predict the correlation between component designs and critical parameters of PEMECs. It is found that the water saturation and current density are not evenly distributed, which significantly depends on the interaction among anode bipolar plates (BPs), porous transport layers (PTLs), and thickness of PEMs. On one hand, the wide lands of anode BPs will partially block the pores of PTLs and cause a severe local dehydration and current density drop, which can be addressed by decreasing the width of BP lands or a flow enhanced liquid/gas diffusion layer (FELGDL) design. On the other hand, a thinner PEM tends to cause a worse uniformity of water and current density distribution in PEMs, though better cell performance is promised. Overall, the presented model provides much localized insights and their impacts on the overall performance of PEMECs, which helps the component design and integration of PEMECs in the future.

Development of high voltage lithium-ion batteries (LIBs) is the most significant to electrifying the aircraft (eVTOL), electric vehicles, and large-scale high-power energy storage systems compared to present LIBs, which are voltage-limited at 4.2 V [1–3]. Spinel LiMn1.5Ni0.5O4 cathode is a promising candidate to supply Li+ ions at high voltage (> 4.2 V) for LIBs [4]. Even though several significant approaches have been devoted in the literature [5-7], commercialization of spinel LiMn1.5Ni0.5O4 cathode is very challenging and requires advanced research studies to attain long-term cycle stability and high-rate performance. Researchers at the University of Tennessee have developed a primary nanoparticle LiMn1.5Ni0.5O4 cathode with surface coating and networking architecture, capable of cycle durable, high-rate performance for high-voltage LIBs, by precursor structural advancement. Batteries with this cathode delivered discharge capacity of 100 mAh g–1 for the 12th cycle and 86 mAh g–1 for the 1000th cycle with minimized capacity fade at 20 C discharge rate [8]. To support the commercialization of UTK-LiMn1.5Ni0.5O4 cathode, electrochemical and thermal stability studies are performed for segregated primary nanoparticles with surface coating-networking architecture, as described in Figure 1. After stabilization of charge and discharge cycles at 1 C, we demonstrate 24 h rest at 100% state of charge (SOC), i.e. 4.9 V, which exhibited no significant changes in the voltage profiles and capacity performance, as shown in Figure 1a. Cyling studies continued with 24 h rest at fully-charged state (4.9 V) repeated for 1 to 30 cycles (Figure 1b) and extended the rest time for 168 h (1 week rest). From the observed voltage profiles and the charge- discharge capacity performance associated with 24 h/ 168 h rest, it is realized that the segregated primary nanoparticle LiMn1.5Ni0.5O4 cathode with surface coating and networking architecture are stable in presence of electrolyte containing 98% of 1M LiPF6 in EC+DEC (1:1 vol%) and 2% of FEC additive. To examine the thermal safety aspects of primary nanoparticles, in situ multimode calorimetry analyses [9] were carried out for the segregated primary nanoparticle LiMn1.5Ni0.5O4 cathode. The MMC results of the cathode at 100% SOC shows no exothermic peak or heat energy release as temperature ramped from RT to 300 °C; this observation confirms that the cathode material is thermally stable in presence of electrolyte (Figure 1c). The in situ MMC analysis of Li-ion full-cell (graphite vs. LiMn1.5Ni0.5O4 cathode, CR2032) at charge state was performed by increasing temperature, as given in Figure 1d. After SEI decomposition at 110 °C, suddenly the cell voltage dropped to 0 V, exhibiting a lower exothermic peak with less released heat energy at 235 °C during thermal runaway event. From the results of electrochemical and thermal stability studies, it is confirmed that segregated primary nanoparticle LiMn1.5Ni0.5O4 cathode with surface coating and networking architecture is robust towards commercialization for high-voltage Li-ion batteries include eVTOL aircraft, EVs, grid energy storage applications. Acknowledgements Research was sponsored by the DEVCOM Army Research Laboratory (ARL) and was accomplished under Cooperative Agreement Number W911NF2220007. The author Manikandan Palanisamy thanks the Department of Mechanical and Aerospace Engineering, University of Tennessee for financial support. References 1. X. G. Yang, T. Liu, S. Ge, E. Rountree and C. Y. Wang, Joule, 2021, 5, 1644–1659. 2. P. Manikandan, P. Periasamy and R. Jagannathan, J. Mater. Chem. A, 2013, 1, 15397–15405. 3. M. Palanisamy, M. H. Parekh, and V. G. Pol, Adv. Funct. Mater., 2020, 30, 2003668 (1–14). 4. Yu. Xingwen, Yu. Wiley A, A. Manthiram, Small methods, 2021, 5, 2001196. 5. S. Li, G. Ma, B. Guo, Z. Yang, X. Fan, Z. Chen and W. Zhang, Ind. Eng. Chem. Res., 2016, 55, 9352–9361. 6. F. Zou, Z. Cui, H. C. Nallan, J. G. Ekerdt and A. Manthiram, ACS Appl. Energy Mater., 2021, 4, 13297–13306. 7. Z. Zhu, D. Zhang, H. Yan, W. Li and Qilu, J. Mater. Chem. A, 2013, 1, 5492–5496. 8. M. Palanisamy and M. M. Mench, Adv. Energy Mater., 2025, 2404368 (1–16). 9. M. Palanisamy, K. W. Lin, C. T. Lo, and V. G. Pol, ACS Appl. Mater. Interfaces, 2022, 14, 28310−28320. Figure 1

This study investigates the path-dependent degradation in polymer electrolyte fuel cells (PEFCs) using two accelerated stress test (AST) protocols derived from the U.S. Department of Energy (DOE) guidelines. The first protocol, PtfCC AST, involved 15,000 cycles of square-wave voltage cycling (0.6-0.95 V vs. reversible hydrogen electrode, RHE) followed by 2500 cycles of triangular-wave voltage cycling (1.0-1.5 V vs. RHE). The second protocol, CCfPt AST reversed the order of execution of triangular-and square-wave cycling. Multimodal characterization techniques, including spatially resolved current distribution and post-mortem micro-X-ray diffraction (micro-XRD) platinum particle size mapping, revealed significant differences in degradation patterns. Different polarization performance (spatially distributed and averaged), electrochemically-active surface area (ECSA) loss, morphological changes, and Pt particle size maps of the active area at the end-of-life (EOL) for the same cumulative stress cycles indicate path dependency of degradation in PEFCs for the two tested protocols and the set of materials. The findings from this study highlight the complex interplay of degradation mechanisms, which are crucial for improving PEFC durability and predictive health monitoring in real-world applications with irregular cycling patterns.

In recent years, many researchers have focused on developing platinum-free catalysts for the oxygen reduction reaction (ORR) [1] due to the high cost and limited availability of platinum. Transition metal oxides present a promising alternative to this precious metal and are being explored for their potential in ORR catalysis 2], particularly in alkaline electrolytes. These oxides can serve as substitutes for platinum-based catalysts, especially in applications in metal-air batteries, including aluminum-air batteries. Moreover, catalysts at the nanometer scale demonstrate enhanced catalytic activity owing to their high surface area. Research indicates that both the size and shape of these nanocatalysts significantly influence their catalytic performance. In this work, we present the synthesis conditions and characterization of manganese oxide nanoparticles (Mn3O4, also known as hausmannite) with various sizes and morphologies.[3][4] these nanocatalysts were subsequently tested for electrochemical activity at room temperature and atmospheric pressure in an O2-saturated 0.1 M KOH solution. We demonstrate that the size and shape of these nanoparticles influence their catalytic activity towards ORR. References [1] Chandran, P., Ghosh, A. & Ramaprabhu, S. High-performance Platinum-free oxygen reduction reaction and hydrogen oxidation reaction catalyst in polymer electrolyte membrane fuel cell. Sci Rep 8, 3591 (2018) [2]Goswami, C., Hazarika, K. K. & Bharali, P. Transition metal oxide nanocatalysts for oxygen reduction reaction. Mater. Sci. Energy Technol. 1, 117–128 (2018). [3]T. Rhadfi, J.-Y. Piquemal, L. Sicard, F. Herbst, E. Briot, M. Benedetti, A. Atlamsani, Polyol-made Mn3O4 nanocrystals as efficient Fenton-like catalysts, Appl. Catal. A 386 (1) (2010) 132–139. [4] Rhadfi, T.; Sicard, L.; Testard, F.; Taché, O.; Atlamsani, A.; Anxolabéhère-Mallart, E.; Le Du, Y.; Binet, L.; Piquemal, J.-Y. J. Phys. Chem. C 2012, 116, 5516

Iridium (Ir)-based catalysts are among the most promising candidates for oxygen evolution reactions (OERs) due to their high activity and durability in electrolysis technology. Traditionally, Ir catalysts are prepared as powders, mixed with supports and binders, and then applied to membranes or substrates. However, this approach often results in significant catalyst waste and the formation of thick catalyst layers that hinder mass transport and performance. Electrodeposition (ED) of Ir onto a porous transport layer (PTL) offers a simple and cost-effective method to fabricate porous transport electrodes (PTEs). This process eliminates the need for ionomers, reduces catalyst loading, and enhances overall performance. Despite its advantages, the mechanisms governing Ir ED for OER applications remain largely unexplored. In this study, the in-situ ED approach to metallic Ir is optimized and the underlying deposition mechanisms are explored. First, we examine how catalyst morphology can be tailored by adjusting the applied potential and modifying the substrate with a seeding layer. Our results show that lower deposition potentials yield smaller catalyst particle sizes, while an Au seeding layer improves adhesion, leading to a denser catalyst structure. Second, we investigate the Ir deposition rate and derive its correlation with the deposition potential. Third, we characterize the performance of electrodeposited Ir electrodes, demonstrating a strong correlation between morphology, deposition potential, and catalytic activity. Additionally, the OER performance is improved by using cyclic voltammetry (CV) to convert the electrodeposited metallic Ir to Ir hydroxides/oxides which favor absorbing the oxygen intermediates. This work provides valuable insights into electrodeposition of PTEs for Ir-based catalysts with controlled morphology and improved OER performance.

To develop cost-effective and high-performing polymer electrolyte water electrolyzers (PEWEs) for gigawatt-scale applications, researchers have focused on reducing precious metal catalyst loadings and optimizing porous transport layers. However, the performance of PEWEs is also affected by system architecture. Mass transport losses are dependent on localized architecture and material interactions. In-situ measurements, such as current density distribution maps have demonstrated advantages in understanding the intricate characteristics and influence of two-phase flow within PEWEs. This study proposes the parameter of effective water transport number (EWTN) as a quantitative tool to investigate such current density distribution (CDD) measurements for PEWEs. Results show that higher flow-rates have EWTN values of 0.95 and above, indicating no mass transport limitations; while lower flow-rates with large gradients CDD have EWTN values between 0.6-0.8, indicating mass transport limited conditions. The new analysis also identified a correlation between mass transport losses due to bubble accumulation, membrane hydration, and ohmic overpotentials. To address these limitations, an unitized pin-type LGDL/flow-field design was developed, which effectively prevents local gas phase accumulation, resulting in improved mass transport characteristics. The results of this work show reduced flow-rate sensitivity with the pin-type architecture and ∼13% increased performance at 0.24 ml / min / cm 2 .

Polymer electrolyte water electrolyzers (PEWEs) are pivotal in the transition to a clean energy economy, promising green and efficient hydrogen production. Understanding the complexities of overpotentials within PEWEs is crucial for optimizing their performance and efficiency 1 . For PEWEs to attain the highest possible system efficiency, considering a specific material set and operating parameters, meticulous design is imperative. The goal is to achieve a high reaction rate that is not only optimal but also uniform across the entire active surface area of the electrodes. This uniformity should ideally be maintained with minimal sensitivity to variations in operating conditions. This study focuses on the contribution of different overpotential categories and reveals their spatial variations through in-situ analysis to understand and overcome the issues caused by non-uniformity in reaction. Employing a segmented cell and printed circuit board (PCB) approach 2 , current density distribution (CDD) and distributed area-specific resistance (DASR) measurements are obtained, enabling a detailed examination of the mass transport overpotentials (as shown in Figure 1). Typically, in the fuel cell community, modeling mass transport limitations is thought of as diffusion-limited transport 3 . In the anode porous transport layer (PTL), oxygen accumulation (i.e. product transport limitation) can cause membrane dry-out and an increase in ASR 4 . The experimental results elucidate the intricate relationship between ohmic and mass transport losses, emphasizing the deep coupling induced by the two-phase nature of the system. Figure 1 shows that, as mass transport limitation grows, the highest increase in overpotential comes from mass transport-coupled ohmic losses. Beyond conventional diffusion limited mass transport losses, bubble dynamics significantly impact local hydration and ASR, highlighting the need for a holistic approach in device optimization 5 . This research contributes to the understanding of PEWE dynamics, providing a basis for informed engineering decisions. By unraveling the intricate interdependencies between overpotentials, this work empowers the efficient utilization of expensive catalyst materials. Moreover, it offers insights into mitigating the challenges associated with bubble removal, accomplishing this with lower pumping requirements that scale non-linearly. These insights enrich both theoretical understanding and are paramount for enhancing system efficiency and economic viability of PEWEs, thereby advancing the prospect of sustainable hydrogen production. Reference N. Danilovic and I. Zenyuk, Electrochem. Soc. Interface , 30 (2021). F. H. Roenning, A. Roy, D. S. Aaron, and M. M. Mench, J. Power Sources , 542 , 231749 (2022) https://linkinghub.elsevier.com/retrieve/pii/S037877532200742X. A. Z. Weber et al., J. Electrochem. Soc. , 161 , F1254–F1299 (2014) https://iopscience.iop.org/article/10.1149/2.0751412jes. C. Immerz, B. Bensmann, P. Trinke, M. Suermann, and R. Hanke-Rauschenbach, J. Electrochem. Soc. , 165 , F1292–F1299 (2018). P. Satjaritanun et al., iScience , 23 , 101783 (2020) https://doi.org/10.1016/j.isci.2020.101783. Figure 1