High-pressure Membrane Research Articles

Heat and Mass Transfer Study of a High-Pressure Membrane Dehumidifier Under Non-Isothermal and Humid Sweep Psychrometric Conditions

Abstract High-pressure membrane dehumidification is of interest for aircraft environmental control system applications. Typically, membrane dehumidifier modules are characterized by manufacturers over a range of mass flow rates, temperatures, and pressures at saturation conditions. However, to evaluate the suitability of high-pressure membrane dehumidification for aircraft applications, the performance must be characterized over the broader range of psychometric conditions that could be encountered. Moreover, the practical integration of a membrane dehumidifier into an environmental control system necessitates reconsideration of the traditional product sweep approach, where some of the dry air produced is removed and supplied to the other side of the membrane to enhance mass transfer. In an environmental control system, using product sweep would require excessive bleed air from the engine and cause unbalanced flow in the turbomachinery. To avoid this, alternate sources of sweep must be considered and their effects on dehumidification must be evaluated. This work conducts an experimental investigation of a membrane dehumidifier module using product sweep under a range of psychometric conditions, then compares product and humid sweep modes to understand the effects of sweep conditions on dehumidification performance. Concurrently, a numerical model of a membrane dehumidifier is implemented and validated - first against the module specification sheet, then against the empirical results that represent moderate altitude aircraft conditions. Ultimately, the feasibility of a hot and humid sweep source to maintain sufficient dehumidification performance under realistic altitude conditions is demonstrated.

Simulation study on preventing explosive mixture formation in PEM electrolysers’ water recovery tanks

Investigations of safety issues related to the design and operation of high-pressure proton exchange membrane (PEM) water electrolysers have until now mainly focused on the electrolyser stack. The present study focuses on the risk of explosive mixture formation in the water recovery system, which is part of the balance of plant in water electrolysers. After a major electrolyser company experienced an unexpected detonation in their system, we analysed their process design as a base case: a low-pressure buffer tank where anodic and cathodic water is mixed with make-up deionised water poses a safety risk because an explosive gas mixture is likely to form there, resulting in severe accidents. Several retrofit options are explored using dynamic and steady-state simulation models: these options are then evaluated based on their effects on safety, general economics and operation of the plant, in addition to ease of retrofit. The results show that preventing the formation of explosive gas mixtures in the water recovery system is achievable in several ways, such as avoiding recycling cathodic water altogether, stripping it of hydrogen, flushing buffer tanks with nitrogen or oxygen, rearranging the balance of plant appropriately, or changing the control algorithms of the system.

Removal of Heavy Metals from Wastewaters and Other Aqueous Streams by Pressure-Driven Membrane Technologies: An Outlook on Reverse Osmosis, Nanofiltration, Ultrafiltration and Microfiltration Potential from a Bibliometric Analysis.

A bibliometric study to analyze the scientific documents released until 2024 in the database Scopus related to the use of pressure-driven membrane technologies (microfiltration, ultrafiltration, nanofiltration and reverse osmosis) for heavy metal removal was conducted. The work aimed to assess the primary quantitative attributes of the research in this field during the specified period. A total of 2205 documents were identified, and the corresponding analysis indicated an exponential growth in the number of publications over time. The contribution of the three most productive countries (China, India and USA) accounts for more than 47.1% of the total number of publications, with Chinese institutions appearing as the most productive ones. Environmental Science was the most frequent knowledge category (51.9% contribution), followed by Chemistry and Chemical Engineering. The relative frequency of the keywords and a complete bibliometric network analysis allowed the conclusion that the low-pressure technologies (microfiltration and ultrafiltration) have been more deeply investigated than the high-pressure technologies (nanofiltration and reverse osmosis). Although porous low-pressure membranes are not adequate for the removal of dissolved heavy metals in ionic forms, the incorporation of embedded adsorbents within the membrane structure and the use of auxiliary chemicals to form metallic complexes or micelles that can be retained by this type of membrane are promising approaches. High-pressure membranes can achieve rejection percentages above 90% (99% in the case of reverse osmosis), but they imply lower permeate productivity and higher costs due to the required pressure gradients.

Enhancing silica scaling resistance of high-pressure reverse osmosis membranes through surface grafting with various sulfonic acid monomers

Silica scaling is a major challenge in the application of high-pressure reverse osmosis (RO) membranes. In this work, we modified commercially available RO membranes by grafting different sulfonic acid monomers onto their surface using redox polymerization. We systematically studied the effects of various sulfonic acid monomers on membrane performance. Due to the different grafting abilities of sulfonic acid monomers on the membrane, the modified membranes exhibited different physicochemical properties. Simulated silica scaling experiments revealed that the initial permeate flux and sulfonic acid grafting rate of the membrane played crucial roles in its antifouling performance. Molecular dynamics (MD) simulation indicated that the adsorption of silica scale on the membrane was positively correlated with the grafting degree of sulfonic acid monomers. The membrane modified with 3-sulfopropyl potassium methacrylate (SPM) demonstrated a 14 % higher initial flux than the pristine membrane and the highest sulfonic acid grafting rate, resulting in the lowest flux decay rate. Additionally, the SPM modified membrane outperformed the pristine membrane against composite foulants with organic matters and silica. Our research demonstrated that the redox grafting polymerization of sulfonic acid monomers can simultaneously improve the flux and silica scaling resistance of RO membranes without compromising salt rejection. This provides a scalable strategy for preparing RO membranes with enhanced resistance to silica scaling.

Rejection of PFAS and priority co-contaminants in semiconductor fabrication wastewater by nanofiltration membranes

Use of high-pressure membranes is an effective means for removal of per-and polyfluoroalkyl substances (PFAS) that is less sensitive than adsorption processes to variable water quality and specific PFAS structure. This study evaluated the use of nanofiltration (NF) membranes for the removal of PFAS and industry relevant co-contaminants in semiconductor fabrication (fab) wastewater. Initial experiments using a flat sheet filtration cell determined that the NF90 (tight NF) membrane provided superior performance compared to the NF270 (loose NF) membrane, with NF90 rejection values exceeding 97 % for all PFAS evaluated, including the ultrashort trifluoromethane sulfonic acid (TFMS). Cationic fab co-contaminants diaryliodonium (DIA), triphenylsulfonium (TPS), and tetramethylammonium hydroxide (TMAH) were not as highly rejected as anionic PFAS likely due to electrostatic effects. A spiral wound NF90 module was then used in a pilot system to treat a lab solution containing PFAS and co-contaminants and fab wastewater effluent. Treatment of the fab wastewater, containing high concentrations of perfluorocarboxylic acids (PFCAs), including trifluoroacetic acid (TFA: 96,413 ng/L), perfluoropropanoic acid (PFPrA: 11,796 ng/L), and perfluorobutanoic acid (PFBA: 504 ng/L), resulted in ≥92 % rejection of all PFAS while achieving 90 % water recovery in a semi-batch configuration. These findings demonstrate nanofiltration as a promising technology option for incorporation in treatment trains targeting PFAS removal from wastewater matrices.

Real-time data acquisition inside high-pressure PEM water electrolyzer

This study used the micro-electro-mechanical systems (MEMS) technology to develop a high-pressure resistant flexible 7-in-1 microsensor (voltage, current, humidity, temperature, pressure, flow, and hydrogen). The microsensor is integrated with a flexible printed circuit (FPC) for real-time data acquisition of local voltage, current, humidity, temperature, pressure, flow, and hydrogen variations in different positions inside a high-pressure proton exchange membrane water electrolyzer (PEMWE). The goal of developing such microsensor is to observe the influence of temperature and pressure on the PEMWE. The operational safety of hydrogen is ensured by using a micro hydrogen sensor.

Development and assessment of a novel isobaric compressed hydrogen energy storage system integrated with pumped hydro storage and high-pressure proton exchange membrane water electrolyzer

In the work, a novel isobaric compressed hydrogen energy storage system integrated with pumped hydro storage and high-pressure proton exchange membrane water electrolyzer is proposed to improve system performance. By integrating pumped hydro storage, the gas storage chamber can operate with a constant pressure at a counter-hydraulic pressure, enhancing the effectiveness and energy storage density of the system. Utilizing high-pressure proton exchange membrane water electrolyzer technology directly to produce high pressure hydrogen and oxygen simplifies the system structure by eliminating the need for gas compressors and cooling unit, thereby improving system stability. Additionally, insulated storage reservoirs are employed in the proposed system to store working fluids, maximizing system performance by minimizing potential waste heat losses. Furthermore, the electrical, thermal, and exergy efficiencies, as well as energy storage density of the proposed system, are assessed using thermodynamic techniques. The results indicate that the round-trip electrical efficiency, round-trip thermal efficiency, round-trip exergy efficiency, and energy storage density of the system can reach 35.39%, 81.03%, 37.89% and 53.46 kWh/m3, respectively. Lastly, parametric studies are conducted to further evaluate system performance under various working conditions.

Site-selective protonation enables efficient carbon monoxide electroreduction to acetate

Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical––but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C2+) products to a single valuable product––an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper catalyst that shows an acetate Faradaic efficiency (FE) of 75% with ultralow HER (<0.2% H2 FE) at 150 mA cm−2. We develop a high-pressure membrane electrode assembly system to increase CO coverage by controlling gas reactant distribution and achieve 86% acetate FE simultaneous with an acetate full-cell energy efficiency (EE) of 32%, the highest energy efficiency reported in direct acetate electrosynthesis.

Effect of granular activated carbon adsorption on mitigating microfiltration membrane fouling by algal organic matter

Abstract Algal blooms can seriously affect the operation of water treatment processes including low-pressure (micro- and ultrafiltration) and high-pressure (nanofiltration and reverse osmosis) membranes mainly due to the accumulation of algae-derived organic matter (AOM). This study investigated the effect of granular activated carbon (GAC) pretreatment on PVDF microfiltration performance for the removal of AOM. Dissolved organic matter (DOM) solution of commercial humic acid, extra- and intracellular organic matter from two species of algae, and Cyanobacteria were used for the investigation of the fouling potential of the membrane. A comparison study of different DOM removal and fouling behaviors of microfiltration (MF) after GAC adsorption as pretreatment was evaluated under variable GAC dosage and solution pH. Almost 15–20% improvement in flux and decline in irreversible fouling occurred due to the pretreatment using 1.0 g/L of GAC for an hour. The intracellular material caused higher membrane fouling than humic acid due to the hydrophilic nature of the AOM. Membrane fouling and decline in flux increased with increasing pH in the range of 5.0–8.0. The comparison results might help to provide insights into the real challenge of dealing with the treatment of algal-laden water.

Rejection of perfluoroalkyl acids by nanofiltration and reverse osmosis in a high-recovery closed-circuit membrane filtration system

Poly- and perfluoroalkyl substances (PFASs), especially perfluoroalkyl acids (PFAAs), have garnered broad attention due to their near ubiquitous presence in environmental and biological matrices, recalcitrant nature, and reported negative human health impacts. Processes using high-pressure membranes such as reverse osmosis (RO) and nanofiltration (NF) have been investigated as PFAA treatment technologies due to their ability to separate dissolved solutes such as inorganic ions, and small molecular weight organic compounds. The major drawback associated with high-pressure membranes is management of the concentrate stream produced during treatment. As a result, high recovery membrane system configurations have been developed with the goal of minimizing volume of concentrate requiring disposal. In the context of PFAS treatment, high-recovery membrane applications may be beneficial; PFAS residuals could be concentrated allowing advantages in terms of disposal, e.g., more effective application of PFAS destruction technologies. The objective of this study was to evaluate the PFAA rejection performance of commercially available high-pressure membranes in a pilot-scale closed-circuit membrane filtration (CCMF) system. The rejection of nine PFAAs by four spiral wound membrane products spanning characteristics ranging from loose NF to seawater RO was investigated during and through two closed-circuit sequences each operating up to 97% recovery. Mechanisms of PFAA rejection including steric and electrostatic exclusion were investigated through analysis of generated data, and ionic strength experiments. Additionally, short-term foulant accumulation during CCMF and normalized energy analysis were performed by monitoring the calculated temperature corrected specific flux (TCSF) and design software simulations, respectively. Results from this study demonstrate that tight NF and RO membranes are effective for separating and concentrating PFAAs during high recovery CCMF operation. During CCMF sequences to 97% water recovery, the NF90, CR100, and SW30 membranes evaluated exhibited overall rejection values of > 98.3% for the PFAAs quantified in this study. The loose NF membrane element investigated (NF270) exhibited the lowest PFAA rejection performance during the high recovery experiments, particularly at water recoveries > 90%. Diminished PFAA rejection performance of the NF270 is likely a result of both steric and electrostatic exclusion being significant separation mechanisms. Feed water amended with sodium sulfate yielded lower rejection for PFAAs by the NF270 compared to unamended feed water supporting the hypothesis that that high recovery CCMF operation may negatively impact PFAS rejection by loose NF membranes, particularly membranes that rely on electrostatic exclusion for separation of anions.

Closing the loop of membranes by recycling end-of-life membranes: Comparative life cycle assessment and economic analysis

Membrane technology has been widely adopted in various industries. However, the inappropriate disposal of end-of-life (EoL) membrane is an urgent issue impeding the sustainability of membrane technology. Herein, we proposed a closed-loop pattern for membrane use by employing upcycling EoL low-pressure membranes and downcycling EoL high-pressure membranes. Life cycle assessment and economic analysis showed that applying the closed-loop recycling strategy could reduce the environmental impacts by 22–27%, in which 24% CO2-eq emissions would be saved with about 27.1% economic advantages, thanks to the reduction of new membrane production and EoL membrane disposal. Sensitivity analysis indicated that more benefits would be achieved through membrane recycling if the project lifetime or the recycled membrane lifetime were extended. Monte Carlo analysis suggested that the closed-loop scenario had less potential to create more environmental impacts than the non-recycling scenario. These results implied that the closed-loop recycling pattern provided a promising paradigm for sustainable membrane application.

Protein Extraction, Precipitation, and Recovery from Chlorella sorokiniana Using Mechanochemical Methods

Protein extraction, precipitation, and recovery methods were evaluated by this study using a green alga—Chlorella sorokiniana. A mechanochemical cell disruption process was applied to facilitate protein extraction from microalgal biomass. Optimization of the mechanochemical process resulted in milling conditions that achieved a protein extraction of 52.7 ± 6.45%. The consequent acid precipitation method was optimized to recover 98.7% of proteins from the microalgal slurry. The measured protein content of the protein isolate was 41.4% w/w. These results indicate that the precipitation method is successful at recovering the extracted proteins in the algal slurry; however, the removal of non-protein solids during centrifugation and pH adjustment is not complete. The energy balance analysis elucidated that the energy demand of the protein extraction and recovery operation, at 0.83 MJ/kg dry algal biomass, is much lower than previous studies using high-pressure homogenization and membrane filtration. This study concludes that mechanochemical protein extraction and recovery is an effective, low-energy processing method, which could be used by algal biorefineries to prepare algal proteins for value-added chemical production as well as to make algal carbohydrates and lipids in the residual biomass more accessible for biofuel production.

Offshore decarbonation of CO2-rich natural gas intensified via gas-liquid membrane contactors with blended aqueous-amines

A battery of high-pressure countercurrent gas-liquid membrane contactors (GLMC) using aqueous-methyl-diethanolamine(39% w/w)-piperazine(5% w/w) solvent is demonstrated for offshore decarbonation of 5MMNm3/d carbon-dioxide-rich natural gas. To accomplish this, a Gas-Liquid Membrane Contactor Unit Operation Extension (GLMC-UOE) was built for HYSYS simulator. Mass/energy balances, pressure-drop, vapor/liquid equilibrium properties are solved by GLMC-UOE with rigorous thermodynamics provided by the HYSYS Acid-Gas Chemical-Solvents Package appropriate for high-pressure carbon dioxide chemical-absorption. GLMC-UOE discretizes a countercurrent GLMC module as a cascade of countercurrent GLMC elements, which are solved via adapted simultaneous corrections of variables. Each GLMC element adopts a multicomponent interfacial heat/mass transfer model based on logarithmic-mean of transmembrane temperature-difference and component fugacity-differences for vapor-to-liquid or liquid-to-vapor transfers. The transferable species comprehend carbon dioxide, methane, ethane, propane, water, methyl-diethanolamine and piperazine. GLMC-UOE was validated against the literature. The process comprises the high-pressure GLMC battery, reboilered low-pressure stripping column, heat exchangers, multi-staged carbon dioxide compression and triethylene-glycol dehydration unit. A stripper heat-ratio of 167.7 kJ/molCO2 was required for solvent regeneration, a value compatible with the literature. The process dispatches dry dense carbon dioxide for enhanced oil recovery in the same offshore field. GLMC-UOE correctly predicts GLMC temperature effects, gas hydration, methane losses in the solvent and pressure-drop.

Flexible Seven-in-One Microsensor Embedded in High-Pressure Proton Exchange Membrane Water Electrolyzer for Real-Time Microscopic Monitoring

The voltage, current, temperature, humidity, pressure, flow, and hydrogen in the high-pressure proton exchange membrane water electrolyzer (PEMWE) can influence its performance and life. For example, if the temperature is too low to reach the working temperature of the membrane electrode assembly (MEA), the performance of the high-pressure PEMWE cannot be enhanced. However, if the temperature is too high, the MEA may be damaged. In this study, the micro-electro-mechanical systems (MEMS) technology was used to innovate and develop a high-pressure-resistant flexible seven-in-one (voltage, current, temperature, humidity, pressure, flow, and hydrogen) microsensor. It was embedded in the upstream, midstream, and downstream of the anode and cathode of the high-pressure PEMWE and the MEA for the real-time microscopic monitoring of internal data. The aging or damage of the high-pressure PEMWE was observed through the changes in the voltage, current, humidity, and flow data. The over-etching phenomenon was likely to occur when this research team used wet etching to make microsensors. The back-end circuit integration was unlikely to be normalized. Therefore, this study used lift-off process to further stabilize the quality of the microsensor. In addition, the PEMWE is more prone to aging and damage under high pressure, so its material selection is very important.

Hydrogen crossover measurement and durability assessment of high-pressure proton exchange membrane electrolyzer

The crossover of hydrogen in a high pressure proton exchange membrane (PEM) hydrogen electrolyzer needs to be taken into account because it affects both energy consumption and safety. And hydrogen crossover measurements at actual operating temperature and pressure conditions are necessary. Hydrogen crossover rates based on pressure data at a cathode pressure of 11.3 MPa, an anode pressure of atmospheric pressure, and a current density of 0.4 A/cm2 have been studied to evaluate the potential of operating a high pressure differential PEM electrolyzer. The degradation phenomenon of the electrolyzer before and after the high pressure experiments has been investigated by both performance testing and material morphology characterization. Irreversible plastic deformation due to strong mechanical extrusion and possible impurity adsorption on the surface of the anode catalyst layer result in a significant performance degradation.

Scanning Electron-Raman Cryomicroscopy for Characterization of Nanoparticle-Albumin Drug Products.

Nanomaterials have expanded the use of active pharmaceutical ingredients by improving efficacy, decreasing toxicity, and facilitating targeted delivery. To systematically achieve this goal, nanomaterial-containing drugs need to be manufactured with precision in attributes such as size, morphology, surface chemistry, and composition. Their physicochemical characterization is essential as their attributes govern pharmacokinetics yet can be challenging due to the nature of many nanomaterial-based formulations unless advanced sample fixation and in vitro characterization methods are utilized. Here, different cryogenic and other fixation strategies were assessed, and a novel physicochemical characterization method was developed using scanning electron Raman cryo-microscopy (SERCM). A complex nanoparticle albumin bound paclitaxel (nab-paclitaxel) formulation was chosen as a model drug. Plunge freezing (PF), high pressure freezing (HPF), freeze substitution (FS), and membrane filtration were compared for their influence on size and morphology measurements, and formulation-based variations were quantified. SERCM was introduced as a multiattribute physicochemical characterization platform, and the composition of nanoparticles was confirmed as albumin-paclitaxel complexes. By coupling image-based quantitative analysis with chemical analysis, SERCM has the potential to pave the way for the development of comprehensive tools for assessing injectable and ophthalmic nanomaterial-containing drugs in their native-like state.

Investigation of Pharmaceuticals in Sakarya Sewage Wastewater

Active substances of drugs can cause various adverse effects by accumulating in the ecosystem. Many medications are resistant to biodegradation, given the recipient media in conventional wastewater treatment plants, and are thus released into the environment after only partial purification or no purification at all. The study focuses on 13 different pharmaceutical compounds belonging to drug classes of anti-depressants, antiepileptic’s, anti-inflammatories, beta-blockers, lidocaine, and stimulants. These compounds were selected with reference to the literature as the ones most commonly encountered in domestic wastewater, surface, and groundwater. The presence of these compounds in the wastewater samples from Sakarya sewage and wastewater treatment plant was investigated. For this purpose, composite samples were taken at various sampling points, and duly analyzed. The analysis revealed the presence of the pharmaceutical residues in the sewage waters from Sakarya Municipality. Some of them were still present in the effluent of the treatment plant. On the other hand, fluoxetine, propranolol, and metoprolol drug active ingredients were not detected at any sampling point. Among all the compounds examined, the highest percentage of residues were observed in the case of active caffeine and paracetamol. In the light of these findings, advanced treatment units such as high-pressure membrane systems (including ozonizing, ultrafiltration, and reverse osmosis) can help adsorption rates at the treatment plant, increasing removal efficiency regarding drug compounds.

Design and economic analysis of high-pressure proton exchange membrane electrolysis for renewable energy storage

The proton exchange membrane (PEM) electrolysis with a high-pressure cathode can help avoid the utilization of a hydrogen compressor and improve the efficiency of hydrogen transmission. The economic analysis of the entire process from hydrogen production to transportation was conducted in this study, and the advantages of high-pressure PEM electrolysis were proved. The economic analysis has also illustrated the influence of the cathode pressure and membrane thickness involved in PEM electrolysis on the energy consumption and capital expenditure of the electrolyzer from the perspectives of hydrogen permeability, ohmic impedance, and structural design. Although the output pressure of hydrogen is increased several tens of times, the proper structure and unchanged thickness of the membrane can help satisfy the strength and safety requirements of the electrolyzer simultaneously. In addition, the energy consumption and cost increase associated with the high-pressure electrolyzer can be limited to an acceptable range. The impact of the renewable energy scale on the decision and selection for PEM or ALK is also analyzed; PEM has an advantage over ALK in large-scale renewable energy hydrogen production scenarios because of its own wider upper and lower load limits compared to those of ALK.

Mass transfer study on high-pressure membrane dehumidification applied to aircraft environmental control system

Expected to replace conventional condensing dehumidification, pressure-driven membrane dehumidification is an alternative to the high-pressure air dehumidification in aircraft environmental control system (ECS). A high-pressure membrane dehumidification experiment is conducted on a counter-flow hollow fiber membrane module to investigate the dehumidification performance under various operating conditions including feed flow rate, feed pressure and sweep ratio. The experiment achieves the dehumidification rate of 1007 g/h at highest. Taking account of the variation of mass transfer driving force along the flow direction, the theoretical model reaches a good agreement with the experiment data. Based on the validated model, a numerical simulation study is conducted to explore the detailed mass transfer characteristics. The simulation reveals the outstanding distinction between the high-pressure and normal-pressure membrane dehumidification. Driven by water vapor partial pressure difference, the mass transfer in the latter one is determined by humidity ratio only, while that in the former one depends on humidity ratio and pressure altogether. Various combination modes of multiple membrane modules are also investigated for more flexible arrangement in the compact space of aircraft, and it is found that the pure parallel mode performs the best. Finally, exergy analysis is employed to compare with the condensing method. In comparison, the membrane method performs the less exergy destruction especially at low desired outlet humidity ratio.

High-Pressure-Resistant Flexible Seven-in-One Microsensor Embedded in High-Pressure Proton Exchange Membrane Water Electrolyzer for Real-Time Microscopic Measurement

The high-pressure proton exchange membrane water electrolyzer (PEMWE) used for hydrogen production requires a high-operating voltage, which easily accelerates the decomposition of hydrogen molecules, resulting in the aging or failure of the high-pressure PEMWE. As the high-pressure PEMWE ages internally, uneven flow distribution can lead to large temperature differences, reduced current density, flow plate corrosion, and carbon paper cracking. In this study, a new type of micro hydrogen sensor is developed with integrated flexible seven-in-one (voltage; current; temperature; humidity; flow; pressure; and hydrogen) microsensors.