The water balance in hydroxide-exchange-membrane fuel cells (HEMFCs) is a key challenge for improved performance and durability, intimately linked with the various interfaces and coupled phenomena. For every 4 electrons produced, 4 water molecules are generated in the anode and 2 consumed in the cathode, while electroosmosis transports water across the HEM from the cathode to the anode. Consequently, a concentration gradient drives water back, from anode to cathode. Ineffective water management could lead to cathode dry-out, limiting reaction rate and causing ionomer degradation, or to anode flooding. To address these concerns, it is critical to measure the water transport operando. Herein, a home-built water-flux station is used to measure total water flux during cell operation with different inlet relative humidities and back pressures. Increasing the HEM thickness fourfold decreases the water flux at high current density, and utilizing microporous layers on both the anode and cathode decreases the water flux from the anode to the cathode. However, the most significant variable in changing the water flux was found by increasing the anode back pressure. Furthermore, humidity cycling significantly changed electrochemical performance without affecting the overall water fluxes. These findings can be translated to other devices utilizing an HEM.

Efficient electrochemical energy devices are vital to renewable energy technology, yet coordinating the effective flow of electrons, ions, and chemical species continues to be a major challenge. In conventional proton-exchange membrane fuel cell (PEMFC) catalyst layers, proton and electron transport are supplied separately through percolating carbon networks and ionomer binders, rendering the catalyst largely passive and imposing fundamental trade-offs between reactant accessibility, ionic conductivity, and catalyst activity. Here, we introduce a one-dimensional proton-electron coupled catalyst (PECC) design, a transport-integrated electrocatalyst architecture in which the catalyst itself simultaneously supplies electronic and protonic transport to catalyst active sites. Using this PECC, PEMFCs can have an ionomer-free cathode catalyst layer (CCL), resulting in a dramatic 95

Microbial cell factories (MCFs) have emerged as a sustainable tool for the production of value-added biochemicals. However, developing high-performance MCFs remains a major challenge to fulfill the burgeoning demands of global markets. This study aimed to establish the B. licheniformis cell factory for the cost-effective production of glutamate-derived chemicals by modular metabolic engineering. Initially, the glutamate decarboxylase from E. coli was introduced into B. licheniformis DW2 to construct the artificial gamma-aminobutyric acid (GABA) pathway. By systematically optimizing the central metabolic pathway, boosting the L-Glu synthesis pathway and improving the cofactor NADPH supply, the strain G35/pHY-Pr5u12-gadBE89Q/H465A achieved a remarkable yield of 62.9 g/L of GABA in a 5-L bioreactor, representing the highest yield of 0.5 g/g glucose with a significant 49.3-fold increase. Remarkably, bioinformatics analyses and function verification identified the putative glyoxylate to glycolic acid synthesis pathway and KipR, an inhibitor of the glyoxylate cycle, as the rate- limiting steps in GABA production. Additionally, a versatile and robust platform using engineered B. licheniformis for efficient production of diverse glutamate-derived chemicals was established and the titer of 5-aminolevulinic acid, heme and indigoidine was improved by 5.3-, 4.7- and 1.9-fold, respectively. This study not only facilitates extensive application of B. licheniformis for chemical production, but also sheds light on research to improve the performance of other MCFs.

To elucidate the impact of local interfaces on mass-transport resistance and overall cell performance of low-loaded proton-exchange-membrane fuel cells (PEMFCs), we present a multiscale modeling framework incorporating a novel modified agglomerate model. The model considers three distinct Pt-electrolyte interfaces: Pt on the carbon surface covered by either ionomer or water film and Pt inside carbon nanopores. Detailed mass-transport voltage-loss breakdowns reveal that coupled agglomerate-interface-scale mass transport dominates the mass-transport loss. The ionomer poisons the exterior-Pt surface through suppressing O2 adsorption and intrinsic ORR activity, leading to low current-density performance. Conversely, interior-Pt interface enhances the kinetic performance but limits high current-density performance due to its low interfacial permeability. The exterior-Pt/ water interface demonstrates superior kinetic performance and mass transport, though its practical implementation requires ensuring proton transport. By coupling the multiscale CL properties with ink parameters, the model identifies an optimal I to C ratio of approximately 0.5, a moderate value where the ionomer content is sufficient to guarantee proton transport without fully covering the Pt surface and forming large agglomeration, thus allowing the utilization of the Pt-water interface and avoiding high mass-transport loss. Overall, the model helps unravel limiting phenomena across different operating regimes and provides routes for optimizing performance.

As lower catalyst loading is required to maintain cost efficiency for PEMFCs, O2 transport becomes pivotal due to the spontaneously increased pressure-independent transport resistance. While O2 transport occurs from nanoscale to macroscale, emerging evidence suggests that the interfacial region at atomistic level near catalyst surface dominates the total transport resistance. Extensive experimental efforts have been taken to understand the transport resistance contributions from each level. However, due to the complexity of the multiscale porous structure and the triple-phase interfaces in catalyst layer, coupled with the limited laboratory techniques for probing the interface at nanoscale in MEA, no conclusive correlation has been established across the scales. Mathematical modelling is a promising approach to connect nanoscale interactions with macroscopic phenomena in a computationally efficient manner. In this work, a multiscale modeling study is presented to understand the effect of platinum interfacial transport resistance on cell performance. The Pt interfaces are separately considered as exterior and interior to represent solid carbon and porous carbon situations. Ionomer and SO3 - coverage are considered for the exterior Pt interfaces, and interior Pt is correlated with pore water uptake in terms of Pt utilization, O2 transport, and proton transport. The interface-dependent properties are up-scaled to a 2D MEA cell-level model through a modified agglomerate model framework. The model reasonably predicts the MEA measurements using Pt/Vulcan and Pt/KB with varying interior Pt loading. The ionomer poisoning not only attributes to the site blocking from SO3 - (reducing ECSA) but also from the low O2 solubility at Pt-ionomer interface compared to the water-covered exterior Pt interface. As for the Pt loaded inside the high surface area carbon (HSC) pores, we found a similar O2 interfacial permeability with the Pt-ionomer interface. Possible explanation includes ionomer penetration, confined water structure inside nanopore that hinders the O2 diffusion, or the long diffusion pathway because of the tortuous pore network. We also performed parametric studies to understand how transport at different scales—interface, ionomer film, and agglomerate—affect the total transport resistance. Lastly, a HSC pore water uptake model was integrated into the cell-level model to address the effect of RH and pore size distribution. We examined the optimal HSC pore size distribution that can balance the Pt utilization, proton transport, and oxygen transport at given operation conditions. The model offers guidance for catalyst design by optimizing ink interaction and CL multiscale porous structure.

Refill friction stir spot welding process is difficultly optimized by accurate modeling because of the high-order functional relationship between welding parameters and joint strength. A database of the welding process was first established with 6061-T6 aluminum alloy and DP780 galvanized steel as base materials. This dataset was then optimized using a backpropagation neural network. Analyses and mining of the experimental data confirmed the multidimensional mapping relationship between welding parameters and joint strength. Subsequently, intelligent optimization of the welding process and prediction of joint strength were achieved. At the predicted welding parameter (plunging rotation speed ω1 = 1733 r/min, refilling rotation speed ω2 = 1266 r/min, plunging depth p = 1.9 mm, and welding speed v = 0.5 mm/s), the tensile shear fracture load of the joint reached a maximum value of 10,172 N, while the experimental result was 9980 N, with an error of 1.92

With the increasing development and popularity of smart wearable devices, smart bracelets have become one of the hottest smart devices today. Through a comparative analysis of existing products, this paper proposes improvement strategies in the three main directions of UI and module design, security, and handling of health issues to provide a product that is easier to use and meets the health needs of the elderly. For the direction of UI and module design, it is proposed to add the gesture recognition function and develop it in the direction of non-contact recognition based on the existing technology, and at the same time, use machine learning to achieve personalized recognition. Based on personalized module design, a GPS tracking device is installed to prevent users from being tracked, and a new network module is added to enable users to get in touch with others at a time when they encounter danger in remote areas. Improvement strategies in the security direction include data transmission, storage, and device security. The smart bracelet can use trusted computing for data encryption and storage by adding low-power core and optimizing the data transmission in three paths: local area network (LAN), public network (PN), and the cloud.Regarding health problem processing, it is proposed to achieve fall prevention through scene recognition and optimize the fall detection function through user information. In addition, this paper takes UV irradiation as an example to point out that smart bracelet devices can be added with new indicator detection technology to prevent some diseases. At the same time, a full voice interaction system can be developed to meet the social needs of the elderly.

This work demonstrates the successful additive manufacturing of an in situ-alloyed CoCrFeNi HEA with a single phase (FCC) structure via the laser metal deposition (LMD) technique. In this work, bulk specimens of the CoCrFeNi high entropy alloy (HEA) of size 15 mm × 15 mm × 45 mm were additive-manufactured (AMed). An H320-type additive-subtractive manufacturing all-in-one system with a 2 kW fiber laser with a coaxial nozzle head integrated in a five-axis CNC machine was used. The effect of varying laser powers (1000 W, 1300 W, and 1600 W) on the microstructure and mechanical and electrochemical properties of the AMed HEA specimens was investigated. The AMed specimens were analyzed for their microstructure, elemental distributions, microhardness, and mechanical and electrochemical properties. An increase in the laser power led to a non-uniform cooling rate and non-steady solidification rates of the molten area during the AM process. As a result, the crystal constant decreased, and the microhardness fluctuated within a narrow range across the specimen. Among the three laser powers, the AMed CoCrFeNi HEA at 1300 W had the optimal mechanical properties and the best electrochemical behavior in 3.5 wt.% NaCl solution.

Proton-exchange-membrane unitized regenerative fuel cell (PEM-URFC) is a promising energy storage and conversion device for large-scale and long-term applications. Previous research has primarily focused on materials development studies, with performance and durability not evaluated at relevant conditions. Such an approach becomes insufficient for making URFC technology commercially competitive. In this review, we highlight recent progress on high-performing PEM-URFCs, focusing on electrode engineering, key components, and operating approaches that take realistic operating conditions into consideration. Key components of a membrane electrode assembly (MEA), including catalyst layer, diffusion media, and membrane, which require different optimization strategies, are discussed in this review.

PEM fuel cell (PEMFC) is one of the promising energy conversion devices for emission-free transportation applications. It is beneficial in faster charging and better scalability compared to battery-powered vehicles, making PEMFC a viable option for heavy-duty vehicles which require higher efficiency and longer lifetimes. To economically compete with the combustion engine and improve commercialization, the PEMFC cathode desires optimization in enhancing the utilization of the expensive Pt catalyst. Integration of high-surface-area carbon (HSC) has shown to increase accessible Pt surface by diminishing ionomer poisoning as Pt particles can be loaded inside the nanoscale micropores (<5 nm) that ionomer cannot penetrate due to size restriction. However, separating Pt catalysts from ionomers requires a water pathway to deliver the proton to the interior catalyst surface, leading to RH-dependent electrochemical surface area (ECSA). In this work, we develop a steady-state, isothermal continuum model to study the gas and ions transport within HSC nanopores. The pore is represented as a straight cylindrical channel filled with water with an ionomer domain at the pore mouth serving as a proton reservoir. The ionomer phase contains H + , OH - , and background stationary SO 3 - while the water phase only includes H + and OH - . The Poisson-Nernst-Plank equations describe the flux of ions, and O 2 transport is described by Fick’s law. Non-ideal behaviors including nanoconfinement effects and dielectric saturation are considered in the pore water phase, reflected by corrections in ion chemical potentials, diffusion coefficients of transport species, and dielectric constant. The electrical double layer (EDL) at the water-electrode interface is depicted as discrete finite domains applying the Gouy-Chapman-Stern (GCS) theory, with the oxygen reduction reaction (ORR) occurring at a finite reaction plane at the outer Helmholtz plane (OHP) through both acidic and alkaline reaction pathways. Donnan potential drop is solved at the ionomer-pore water interface and governs potential distribution in the pore water phase, further determining ionic concentrations at the catalyst surface and thus the kinetic region of polarization curves. The strong-adsorbed water adlayers due to nanoconfinement effects create a transport barrier for O 2 approaching the catalyst surface, leading to higher mass transport resistance. A comparison between a flooded pore scenario (only a water phase exists in the pore) and a wetted pore scenario (the pore wall is covered by a water film while a gas phase also exists in the pore) shows that mass transport is hindered in the flooding pore as O 2 dissolves in the pore water through a limited pore-ionomer interfacial area, while pore gas phase in the wetted pore serves as an extra O 2 resource. This suggests that the management of HSC water uptake needs to avoid pore flooding while ensuring enough wettability to allow proton transport. The model is expected to couple with HSC pore size distribution measured from experiments and upscale to a cell-level model in future work.

Unitized regenerative fuel cells (URFCs) convert electrical energy to chemical bonds in hydrogen during charge and convert chemical energy to output electricity during discharge, offering a promising solution to long-term energy storage. Recent studies indicate that the round-trip-voltaic efficiency (RTE) and longevity of URFCs are limited by complex mass transport during charging and discharging. Here, we first investigate how different porous transport layer (PTL) structures can impact URFC performance. The preferred PTL has a low tortuosity and high porosity, leading to a high RTE above 50% at 1 A cm −2 using Nafion 212. Moreover, thicker membranes, such as Solvay 90, are required to ensure mechanical stability and minimize H 2 crossover when operating under high differential pressure. Although this assembly inevitably leads to a higher ohmic loss, the RTE can be improved by further tailoring the electrode structures to facilitate mass transport by using supported catalyst, which still achieves over 50% RTEs at 1 A cm −2 . Optimization of porous structure to mitigate mass transport resistance with appropriate materials down selection considering practical application requirements can be a key design principle for achieving high-performing URFCs.

A Unitized Reversible Fuel Cell (URFC) system provides many benefits for energy storage by combining a fuel cell and an electrolyzer into a single stack, thus simplifying the system while decreasing weight, footprint, and material costs. URFC systems usually have low overall efficiency due to conflicting optimal operating conditions required for electrolyzer and fuel cell. This study optimized the membrane electrode assembly of the proton exchange membrane cell components to achieve 50% round trip efficiency and reliable performance under relevant duty cycles. Several components have been studied in this project including membranes, bifunctional catalysts for oxygen reduction and evolution reactions and porous transport layers (PTL). Different strategies have been applied to increase the overall performance of the stack while maintaining a low degradation rate. In particular, we looked at reducing the thickness of membranes as well as increasing the operating temperature. A comprehensive study of bifunctional catalyst has been carried out by varying the ratio of catalysts suitable for OER and catalysts suitable for ORR. Variation of the hydrophilicity of the PTL has been done to identify the optimum amount in terms of water and gas transport in the layers for both modes of operation.

This work describes the process of preparing 316 L stainless steel powder by vacuum atomization, then a 3D print sample of 316 L stainless steel is prepared by selective laser melting (SLM) experiments. Over 77% of the powder particle size distribution ranges from 15 to 45 μm. The prepared sample shows a smooth surface with few satellite globules and high sphericity with the 4.5 Mpa atomization pressure. Under these atomization pressure conditions, the tensile strength can reach 798 Mpa and the elongation up to 32.3%. This work demonstrated that 3D printing metal materials with high tensile strength and good plasticity could be obtained under appropriate atomization pressure conditions.

Hydrogen based proton-exchange-membrane fuel cells (PEMFCs) provide a sustainable, potentially decarbonized solution to meet the future energy needs for mobility applications especially heavy-duty vehicles. Water management plays a critical role in determining the performance and efficiency of PEMFCs. 1 Low water content in the membrane-electrode assembly (MEA) can lead to membrane dehydration and subsequently increased ohmic overpotentials, while high water content can result in local flooding of the porous media, thereby leading to mass-transport limitations. The structure and properties of the porous media and membrane govern the water transport in the MEA and thus, parameterizing the effect of these properties on the water balance in the MEA is important for the design of next generation materials, a task that mathematical modeling is ideally suited to tackle. In this work, a 2D half-land half-channel MEA model, 2 modified to explicitly include gas crossover, is used to study the effect of different layer properties on PEMFC performance. The model is used to examine both impact of membrane thickness in traditional PEMFCs, as well as water management with thicker electrodes and asymmetric diffusion media with non-platinum-group-metal PEMFCs. For the former, the tradeoffs between crossover and water gradients versus ohmic losses is quantified including explicit membrane-thickness-dependent properties. 3 For the latter, specific cases of diffusion media with different pore size distributions and permeabilities is explored. Water-balance and voltage-breakdown analysis elucidate the design parameters limiting the PEMFC performance. References A. Z. Weber et al., Journal of The Electrochemical Society , 161 , F1254–F1299 (2014). L. M. Pant, S. Stewart, N. Craig, and A. Z. Weber, Journal of The Electrochemical Society , 168 , 074501 (2021). X. Luo et al., Journal of The Electrochemical Society , 168 , 104517 (2021).

Gas molecules and interfaces with liquids and solids play a critical role in living organisms, sorption, catalysis, and the environment. Monitoring adsorption and heterogeneous interfaces remains difficult in experiments, and earlier models for molecular simulations lead to errors over 100% in fundamental molecular properties. We introduce conceptually new force field parameters for molecular oxygen, nitrogen, and hydrogen that reduce deviations to <5%. We employ a combination of a harmonic bond stretching potential and Lennard-Jones parameters with 12-6 and 9-6 options, leading to computed bond lengths, Raman peaks, liquid densities, vaporization enthalpies, and free energies of hydration in impressive agreement with experiments. Reliable free energies of hydration were obtained upon validation of density and vaporization energy without significant further parameter adjustments. We illustrate applications to O2 adsorption on Pt electrocatalysts and N2 adsorption in zeolites, showing <5% deviation in adsorption energies measured in experiments without additional fitting parameters. We discuss the chemical interpretation of all parameters and explain the reasons for discrepancies in earlier models. Compatibility with the Interface Force Field (IFF), CHARMM, AMBER, OPLS-AA, GROMOS, DREIDING, CVFF, PCFF, COMPASS, and QM/MM methods enables reliable simulations of gases and liquid/solid interfaces with biopolymers, minerals, and metals. The parametrization protocol can be applied to similar molecules.

The oxygen reduction reaction (ORR) on platinum catalysts is essential in fuel cells. Quantitative predictions of the relative ORR activity in experiments, in the range of 1 to 50 times, have remained challenging because of incomplete mechanistic understanding and lack of computational tools to account for the associated small differences in activation energies (<2.3 kilocalories per mole). Using highly accurate molecular dynamics (MD) simulation with the Interface force field (0.1 kilocalories per mole), we elucidated the mechanism of adsorption of molecular oxygen on regular and irregular platinum surfaces and nanostructures, followed by local density functional theory (DFT) calculations. The relative ORR activity is determined by oxygen access to platinum surfaces, which greatly depends on specific water adlayers, while electron transfer occurs at a similar slow rate. The MD methods facilitate quantitative predictions of relative ORR activities of any platinum nanostructures, are applicable to other catalysts, and enable effective MD/DFT approaches.

Liquid emulsion droplet evaporation is of importance for various sensing and imaging applications. The liquid-to-gas phase transformation is typically triggered thermally or acoustically by low-boiling point liquids, or by inclusion of solid structures that pin the vapor/liquid contact line to facilitate heterogeneous nucleation. However, these approaches lack precise tunability in vaporization behavior. Here, we describe a previously unused approach to control vaporization behavior through an endoskeleton that can melt and blend into the liquid core to either enhance or disrupt cohesive intermolecular forces. This effect is demonstrated using perfluoropentane (C5F12) droplets encapsulating a fluorocarbon (FC) or hydrocarbon (HC) endoskeleton. FC skeletons inhibit vaporization, whereas HC skeletons trigger vaporization near the rotator melting transition. Our findings highlight the importance of skeletal interfacial mixing for initiating droplet vaporization. Tuning molecular interactions between the endoskeleton and droplet phase is generalizable for achieving emulsion or other secondary phase transitions, in emulsions.

Systematic control of grain boundary densities in various platinum (Pt) nanostructures was achieved by specific peptide-assisted assembly and coagulation of nanocrystals. A positive quadratic correlation was observed between the oxygen reduction reaction (ORR) specific activities of the Pt nanostructures and the grain boundary densities on their surfaces. Compared to commercial Pt/C, the grain-boundary-rich strain-free Pt ultrathin nanoplates demonstrated a 15.5 times higher specific activity and a 13.7 times higher mass activity. Simulation studies suggested that the specific activity of ORR was proportional to the resident number and the resident time of oxygen on the catalyst surface, both of which correlate positively with grain boundary density, leading to improved ORR activities.

We demonstrate the 2-D anisotropic formation of ultrathin free-floating Pt nanoplates from the assembly of small nanocrystals using T7 peptide (Ac-TLTTLTN-CONH2). As-formed nanoplates are rich in grain boundaries that can promote their catalytic activities. Furthermore, we demonstrate that a minor number of Pd atoms can selectively deposit on and stabilize the grain boundaries, which leads to enhanced structure stability. The Pd-enhanced Pt polycrystal nanoplates show great oxygen reduction reaction activities with 15.5 times higher specific activity and 13.7 times higher mass activity than current state-of-the-art commercial Pt/C electrocatalysts as well as 2.5 times higher mass activity for hydrogen evolution reaction compared with Pt/C.