High Relative Humidity Levels Research Articles

Positrons as microprobes to study water-dependent free volume of wood cell walls: a preliminary study

Abstract Positron annihilation lifetime spectroscopy (PALS) was employed to study the water-dependent free volume characteristics of wood cell walls in earlywood and latewood of loblolly pine (Pinus taeda). Measurements were conducted across relative humidity levels (1–80% RH) at room temperature, demonstrating good reproducibility and consistency with polymer science principles. The Tao-Eldrup model was applied to the measured ortho-positronium lifetimes to estimate the mean sizes of free volume elements in wood cell walls. At low relative humidity (below ~ 11%), water absorption resulted in antiplasticization, evidenced by a decrease in mean free volume element sizes. As relative humidity increased, water started acting as a plasticizer, causing the free volume elements to expand. While dry cell walls showed no significant differences in free volume element sizes between earlywood and latewood, earlywood exhibited larger mean free volume element sizes at all higher relative humidity levels. At higher relative humidity levels (above ~ 70% RH), the ortho-positronium lifetimes of cell wall free volume elements overlapped with those of liquid water, indicating PALS cannot provide reliable free volume information at higher cell wall moisture contents. Interpreting the intensity of ortho-positronium annihilation was complicated by the possibility of water inhibiting ortho-positronium formation in wood cell walls.

Carbonation under Varying Humidity Conditions: A 3D Micro-Scale Kinetic Monte Carlo Approach.

This paper investigates the impact of varying humidity conditions on the carbonation depth in hardened cement paste using a 3-dimensional microscale kinetic Monte Carlo (kMC) approach. The kMC algorithm effectively simulates the carbonation process by capturing the interplay between CO2 diffusion and relative humidity at the microscale, providing insights into macro trends that align with historical models. The study reveals that the maximum carbonation depth is achieved at relative humidity levels between 55 and 65%, where the balance between water and CO2 diffusion is optimized. At lower relative humidity levels (<55%), a lower carbonation depth is observed. Conversely, at higher relative humidity levels (>65%), increased water content impedes CO2 diffusion, resulting in reduced carbonation depth for cement paste. The kMC model demonstrates a parabolic relationship between relative humidity and carbonation depth. Time series analysis shows that Fick's law is consistently followed, with carbonation depth following the relationship x = k√t at constant relative humidity. The kMC also breaks down the event cycle which shows that after an equilibrium (in terms of rate of events) is achieved between CO2 and H2O at a relative humidity of 75%, a shift occurs in the dominance from reactive to transport processes at a relative humidity of 85%. These findings highlight the importance of humidity in influencing carbonation rates on the one hand and demonstrate the effectiveness of the kMC approach in simulating these complex interactions at the microscale on the other hand.

Development of smart control system for leakage warning in compact roofs

Smart sensor technologies to monitor temperature and moisture conditions in building components can be used to give automatic warnings for abnormal high levels of moisture. Flat compact roofs are of particular interest in this context, especially due to their vulnerability to rain leakages through the roofing membrane. Installing moisture sensors in such roofs measuring relative humidity (RH) and free water may give an early warning of rain leakages or condensation owing to air leakages from indoors before damage occurs. One challenge is, however, that normal moisture redistribution in the insulation layer over the season or a day may give very high levels of RH in the top or bottom part of the insulation. A sensor system must be able to distinguish between these normal RH levels and leakage events. Together with a sensor technology and control system producer, a semi-quantitative system that defines typical or normal RH levels in the insulation layer of the roof during the year has been developed. To investigate the applicability of such a system, measurements from the compact roofs of two pilot buildings located in Norway have been analysed. The objective has been to identify connections between measured data, occurring climate conditions and seasonal variations. Results may be used to further develop and improve the algorithms of the leakage warning system.

Fresh water production via atmospheric water harvesting using solar energy for green hydrogen production

Abstract Solar energy is used to drive an atmospheric water harvesting unit to produce fresh water needed for the electrolysis process to produce hydrogen, as well as to drive the electrolyzer. So, the system can be considered as a solar powered hybrid system for fresh water harvesting and green hydrogen production implementing the electrolysis concept. Implementation of the system specially in arid regions with high levels of water scarcity and high relative humidity levels helps in achieving SDGs 3, 7, 9, and 13 progressively, improving health and wellbeing, reducing water scarcity, using clean renewable energy, and limiting climate change. The system is proposed and investigated for the production of both fresh and clean water and green hydrogen gas. To improve the productivity of the overall system, performance enhancement of the atmospheric water harvesting subsystem is experimentally investigated to assure the reliability and continuous operation of the overall green hydrogen hybrid system. It was investigated in summer and winter using different number of porous sheet metals with the silica gel bed. The results show that the productivity of the atmospheric water harvesting system can be increased by a minimum of 6% with one mesh metal sheet and 30% with two meshes, and increases by a maxinmum of 60% with one mech and 260% with two meches.

Unveiling the water sorption kinetics, thermodynamics, and air dehumidification performance of sustainably synthesized metal–organic frameworks

This study focuses on the feasibility of sustainably synthesized MIL-100(Fe) as an alternative to conventional desiccants, such as silica gel and zeolites, which have low adsorption capacity and poor thermal characteristics for air dehumidification. MIL-100(Fe), a metal–organic framework, shows promise due to its excellent adsorption and customizable thermal properties. However, its synthesis typically involves toxic materials and high temperature/pressure conditions, which restrict its bulk production for large-scale applications. This study aims to explore sustainable synthesis methods for MIL-100(Fe) using non-toxic materials and milder reaction conditions and investigate its material characteristics and dehumidification performance. Experimental analyses are carried out to measure adsorption isotherms, kinetics, sorption heat, activation energy, and cyclic stability, and numerical simulations are conducted in COMSOL Multiphysics platform to estimate dehumidification performance. The test results demonstrate that MIL-100(Fe) has a higher water adsorption capacity compared to silica gel, with a unique stepwise adsorption into its two types of mesoporous cages. Increased temperatures cause the adsorption and desorption isotherms to shift towards higher relative humidity levels. The heat of water adsorption and desorption ranges between 2630–2906 kJ/kg and 2763–2848 kJ/kg, respectively. MIL-100(Fe) demonstrates high stability and no significant loss in water uptake capacity. The simulated performance indicate that MIL–100(Fe) has superior reaction rates and is 82 % more effective than the silica gel rotary wheel dehumidifiers.

UV light absorption at 370 nm by mineral dust, organic carbon, and elemental carbon in the Himalayas and Tibetan Plateau

The mass and light absorption contributions of organic carbon (OC), elemental carbon (EC), and mineral dust influence glacial melting and potentially contribute to climate change over the high Himalayas and Tibetan Plateau (HTP). Plateau-scale investigations of these components and their respective light absorption are limited due to the high altitude. In this study, we combined the analysis of major light-absorbing substances and their corresponding multiwavelength absorption to determine their specific contributions firstly. We investigated the spatial variations of total suspended particle (TSP) mass across the HTP, noting high contributions from dust, carbonaceous components, and secondary inorganic aerosols (SNA, including sulfate, nitrate, and ammonium). Enhanced levels of primary and secondary OC and SNA were observed in the marginal areas of the HTP, associated with high relative humidity (RH) and OX levels (O3+NO2). EC was the primary contributor to light absorption, accounting for approximately 68%, 46%, and 64% in Ngari, Qinghai Lake, and Beiluhe, respectively. We found higher light-absorbing contributions from carbonaceous aerosols in the marginal areas compared to the central HTP site, particularly during the heating seasons (∼90%). Fugitive dust significantly contributed to TSP mass but not to light absorption. The concurrent constraints on the mass and optical properties of OC, EC, and dust in this study can help reduce uncertainties in climate models specific to the HTP.

Bipolar ionization-mediated airborne virus inactivation and deposition rates

Bipolar ionization (BPI) of indoor air has emerged as a widely implemented bulk-air disinfection technology to reduce human exposure to airborne viruses. This study presents BPI-mediated decay rate constants for the inactivation and deposition of infectious viral aerosols. Rate constants are estimated for the enveloped bacteriophage Ф6, a common SARS-CoV-2 surrogate, at low (∼25 %), medium (∼50 %) and high (∼75 %) relative humidity (RH) levels under bipolar ion concentrations of 106 ions/cm3. Enhanced BPI-facilitated viral inactivation rate constants of 4.6, 6.9, and 7.6 h −1 under low, middle, and high RH, respectively, are reported. BPI-mediated infectious decay and deposition rates for aerosolized Ф6 were RH-dependent, with significant increases from low to high RH (p < 0.05). Calculated BPI susceptibility constants, that account for ion concentrations, reveal limited airborne viral inactivation (<0.1 h −1) at bipolar ion levels (103 ions/cm3) that are common in bulk air where BPI is applied.

Beyond static: Tracking the dynamic nature of water absorption and Young's modulus in IPMC devices

AbstractIonomeric polymer‐metal composites (IPMC) are advanced materials designed to mimic biological systems. Their performance depends on various factors, including electrical stimulus intensity, membrane hydration, ionic migration, and Young's modulus. However, there is a lack of studies in the literature investigating how the water absorption capacity and elastic modulus change over time in IPMCs. Understanding the hydration level variation as a function of time is essential because as this parameter deviates, the ionic migration capacity and Young's modulus also change, altering the device's electromechanical efficiency over time. To address this research gap, Nafion/Pt‐based IPMC devices exchanged with four monovalent cations (H+, Li+, Na+, and K+) and one ionic liquid (1‐butyl‐3‐methylimidazolium—BMIM+) were prepared, and a comprehensive investigation on how the water absorption capacity and Young's modulus vary as a function of time, relative humidity (RH), and counterion size was performed. The results revealed that the water uptake capacity is significantly higher and occurs more rapidly at higher RH levels and when the counterion's ionic radius decreases. Consequently, the time required for the device to reach osmotic equilibrium can range from 40 to 270 min, depending on the RH and counterion used. Furthermore, it was observed that the first natural frequency and Young's modulus also exhibit time‐dependent behavior. Under constant RH conditions, the mechanical properties of the IPMC can vary by up to 50% in less than 60 min. Notably, the combined results from water uptake capacity, Young's modulus, electrochemical impedance spectroscopy, and electromechanical response analyses (including blocking force, displacement, displacement rate, current, coulombic efficiency, and voltage) suggest that a morphological transformation within the polymer is likely to occur once RH exceeds 60%. This finding strengthens the hypothesis that ion migration is mainly influenced by their movement through Nafion's ionomeric channels rather than the filling of ionic agglomerates.

Evaluating the effects of heatwave events on hydrological processes in the contiguous United States (2003–2022)

Extreme heat and drought conditions are affecting water availability in many regions worldwide, leading to negative impacts on human societies, agriculture, and ecosystems. However, current research lacks comprehensive spatiotemporal analysis examining the interplay between multiple hydrological factors and heatwave events, especially in the context of climate change. This research broadly pertains to understanding the dynamics of hydrological factors and their potential responses to heatwave during warm seasons across the contiguous United States for the period from 2003 to 2022. Utilizing data from the Global Land Data Assimilation System (GLDAS), we analyzed surface runoff, evapotranspiration (ET), precipitation, Groundwater Storage (GWS), Root Zone Soil Moisture (RZSM), and Total Water Storage (TWS) to discern annual patterns and the impacts of heatwave. The spatial patterns of heatwave highlighted a higher occurrence in the western, central, and northeastern U.S., with longer average durations in the western and south-central regions. These events are predominantly dry, characterized by low Relative Humidity (RH), except in the southeastern U.S., where heatwave coincide with high RH levels. Post-heatwave analysis indicated a reduction in GWS, TWS, RZSM, and ET, alongside an increase in surface runoff, RH, and precipitation. An in-depth examination of rainfall and temperature dynamics during heatwave revealed weak correlations between rainfall and temperature, as well as between rainfall and heatwave duration, highlighting the complex nature of these interactions. The study also found an enhanced probability of rainfall following heatwave, particularly in the eastern regions, drawing attention to the potential for increased flood risks post-heatwave. Our findings contribute to the growing body of knowledge on the impacts of heatwave on hydrological factors, providing valuable insights for climate change adaptation and water resource management strategies.

Effects of Gas-Diffusion Layers and Water Management on the Carbon Corrosion of a Catalyst Layer in Proton-Exchange Membrane Fuel Cells

Carbon corrosion in a catalyst layer (CL) deteriorates the performance and durability of proton-exchange membrane fuel cells (PEMFCs), which are closely related to water management within these cells. This study investigates the characteristics of water behavior of two gas diffusion layers (GDLs) and compares their influence on degrees of degradation in the CL. First, the properties of the GDLs, including their thickness, pore size distribution, gas permeability, electrical resistance, contact angle, and polytetrafluoroethylene (PTFE) content, are evaluated. The dynamic behavior of liquid water is observed using a visualization cell and synchrotron X-ray imaging. Second, a modified accelerated stress test (AST), which includes a water generation reaction within the catalyst support protocol of the US Department of Energy (DOE), is performed. For assessing the degradation, we utilize polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and field emission transmission electron microscopy. The results reveal that, even though GDL B contains a higher hydrophobic content than GDL A, it exhibits lower water discharge, indicating a reduced performance at high relative humidity (RH) levels. This is attributed to a low capillary pressure gradient, which is influenced not only by PTFE but also by the overall pore structure (i.e., porosity and pore size). Consequently, a high capillary pressure gradient can enhance water discharge and thereby mitigate carbon corrosion and Pt agglomeration in the CL. In addition, the application of the modified AST induces carbon corrosion with fewer cycles than that achieved using the DOE carbon support protocol.

The impact of short-term exposure to meteorological factors on the risk of death from hypertension and its major complications: a time series analysis based on Hefei, China.

This study aimed to reveal the short-term impact of meteorological factors on the mortality risk in hypertensive patients, providing a scientific foundation for formulating pertinent prevention and control policies. In this research, meteorological factor data and daily death data of hypertensive patients in Hefei City from 2015 to 2018 were integrated. Time series analysis was performed using distributed lag nonlinear model (DLNM) and generalized additive model (GAM). Furthermore, we conducted stratified analysis based on gender and age. Relative risk (RR) combined with 95% confidence interval (95% CI) was used to represent the mortality risk of single day and cumulative day in hypertensive patients. Single-day lag results indicated that high daily mean temperature (T mean) (75th percentile, 24.9°C) and low diurnal temperature range (DTR) (25th percentile, 4.20°C) levels were identified as risk factors for death in hypertensive patients (maximum effective RR values were 1.144 and 1.122, respectively). Extremely high levels of relative humidity (RH) (95th percentile, 94.29%) reduced the risk of death (RR value was 0.893). The stratified results showed that the elderly and female populations are more susceptible to low DTR levels, whereas extremely high levels of RH have a more significant protective effect on both populations. Overall, we found that exposure to low DTR and high T mean environments increases the risk of death for hypertensive patients, while exposure to extremely high RH environments significantly reduces the risk of death for hypertensive patients. These findings contribute valuable insights for shaping targeted prevention and control strategies.

Robust Modeling for Factors Affecting in Relative Humidity in Basra Governorate

Basra Governorate is considered among the Iraqi governorates, with high levels of relative humidity sometimes, which makes the weather uncomfortable during the year. It was necessary to building in this research a robust regression model to study the effect of some factors such as the maximum and minimum temperatures, the amount of rainfall, atmospheric pressure, and the average amount of dust falling. When building linear regression models, many problems occur in which failure some of the hypotheses model. In this research, least squares estimates were compared with robust and found the preference for the method of S.

Comprehensive Computational Study on the Influences of Particle Size and Relative Humidity on Aerosol/Droplet Transmission in a Ventilated Room Under Stationary and Dynamic Conditions

Given the concerns surrounding the possibility of crosscontamination caused by the airborne transmission of respiratory aerosols (&gt; 5 μm in diameter) and droplets (&gt; 5 μm in diameter) containing infectious viruses, there is a great need for simulations that reliably characterize the behaviour of these particles in real‐world scenarios. This study performs a comprehensive transient CFD analysis to investigate the transmission of virus‐carrying aerosols and droplets released through coughing by a mobile patient within a typical room equipped with a ventilation system. This computational study elaborately examines how particle size and relative humidity impact the dispersion of aerosols and droplets carrying virus in both mobile and stationary conditions of patients. To enhance the accuracy of this study, effective factors such as evaporation of liquid content within aerosols and droplets and random distribution of the particles, along with considerations for buoyancy, drag, lift, Brownian motion, and gravitational forces, are taken into account. To investigate the influence of aerosol and droplet size, this study considers uniform size distributions of 1, 10, and 100 μm in diameter, comprising 98.2% liquid water and 1.8% solid content. Additionally, different relative humidity levels, 0%, 50%, and 90%, are incorporated to indicate their impact on the dispersion pattern and residence time of the particles in both stationary and dynamic scenarios. According to the results, high levels of relative humidity and individuals’ movement significantly affect the turbulence intensity, airflow pattern, travelling distance, residence time and trajectory of particles, air pressure, and density distributions in such environments.

Development of smart control system for leakage warning in compact roofs

Smart Sensor technologies to monitor temperature and moisture conditions in building components, can be used to give automatic warnings for abnormal high levels of moisture. Flat compact roofs are of particular interest, especially due to their vulnerability to rain leakages through the roofing membrane. Installing moisture sensors in such a roof measuring relative humidity (RH) or free water may give an early warning of rain leakages or condensation due to air leakages from indoors – before they start to get problematic. One challenge is, however, that normal moisture redistribution in the insulation layer over the season or day may give very high levels of RH in the top or bottom part of the insulation. The sensor system must be able to distinguish between these normal levels and leakage events. Together with a sensor technology and control system producer we have previously developed a semi-quantitative system that defines typical or normal RH levels in the insulation layer during the year. This system was based on hygrothermal simulations for various conditions, such as different exterior climate and levels of built-in moisture. This paper presents the preliminary findings from the further development of the system using real measurements from two pilot buildings located in Norway.

Geometric Analysis of Free and Accessible Volume in Atmospheric Nanoparticles.

Computer-generated atomistic microstructures of atmospheric nanoparticles are geometrically analyzed using Delaunay tessellation followed by Monte Carlo integration to compute their free and accessible volume. The nanoparticles studied consist of cis-pinonic acid (a biogenic organic aerosol component), inorganic ions (sulfate and ammonium), and water. Results are presented for the free or unoccupied volume in different domains of the nanoparticles and its dependence on relative humidity and organic content. We also compute the accessible volume to small penetrants such as water molecules. Most of the free volume or volume accessible to a penetrant as large as a water molecule is located in the domains occupied by organics. In contrast, regions dominated by inorganics do not have any cavities with sizes larger than 1 Å. Solid inorganic domains inside the particle are practically impermeable to any small molecule, thereby offering practically infinite resistance to diffusion. A guest molecule can find diffusive channels to wander around within the nanoparticle only through the aqueous and organic-rich domains. The largest pores are observed in nanoparticles with high levels of organic mass and low relative humidity. At high relative humidity, the presence of more water molecules reduces the empty space in the inner domains of the nanoparticle, since areas rich in organic molecules (which are the only ones where appreciable pores are found) are pushed to the outer area of the particle. This, however, should not be expected to affect the diffusive process as transport through the aqueous phase inside the particle will be, by default, fast due to its fluid-like nature.

Worldwide potential of emissive materials based radiative cooling technologies to mitigate urban overheating

Radiative cooling has gained significant attention in recent years for its passive heat evacuation capabilities. Numerous materials have been developed, but comparing their cooling effectiveness has proven challenging due to inconsistent experimental conditions. This study aims to bridge this gap by evaluating the heat evacuation potential of various radiative cooling materials under consistent climatic conditions.Using a validated heat transfer model, the performance of eleven materials was simulated in twenty-two Urban Overheating-affected cities. The assessment considered factors such as radiated heat losses, solar heat gains, and convective heat losses to gauge the cooling power of each material. The simulation assumed an active system where the materials were placed on a highly conductive, uninsulated surface, akin to having a fluid at a constant temperature beneath.The ability of materials to radiate heat and cool down depends on their optical properties. The findings suggest limited benefits in equatorial climates, with an average monthly total heat exchanged (MATHE) of −19.73 kWhm−2. Materials displayed consistent behavior throughout the year in climates with high relative humidity levels. Climates with elevated ambient temperatures derived the greatest advantages from strictly selective and highly reflective materials that emitted within the atmospheric window. Arid climates showed potential during transition times (MATHE -74.5 kWhm−2), while warm temperate climes benefited during summer months (MATHE -112.1 kWhm−2). In snow zone climates, the system could be utilized year-round for cooling-intensive scenarios, with a MATHE of −203.8 kWhm−2. This study evaluates radiative cooling materials' effectiveness in different climates, informing energy-efficient cooling applications.

Assessment of the Correction of the Reference Evapotranspiration at Nonirrigated Weather Stations Affected by Aridity and Delimitation of the Meteorological Conditions that Limit its Implementation

As most reference crop evapotranspiration (ETref) estimates are computed from weather stations located outside irrigated plots, the site aridity can produce ETref overestimation. To obtain more reliable ETref estimates, the potential of using the methodology that corrects the observed air and dew point temperatures was first analyzed in this study, and the meteorological conditions that limit this methodology implementation were subsequently assessed. A statistical analysis was conducted of pairwise comparisons between a station under reference conditions (Montañana) and four nearby stations affected by aridity in Spain for 2020. The daily reference evapotranspiration was calculated with the FAO56 Penman–Monteith equation (ETo PM), and afterward, the corrected daily reference evapotranspiration (ETo PMcor) was obtained using the previously mentioned correction methodology. The statistical analysis showed a greater connection between ETref and ETo PMcor in all pairwise comparisons, with the strongest connection reached between ETref Montañana station and ETo PMcor Pastríz station (coefficient of determination r2 = 0.98 and root mean square error RMSE = 0.34 mm/day.). This ETo PM correction methodology was established considering a difference between the minimum temperature (Tmin) and the dew point temperature (Tdew) greater than 2 °C, as this value is considered the benchmark of aridity, but this research found that high aridity (P/ETo < 0.5) inland locations and high aridity coastal locations with high relative humidity (RH), markedly as of 61.5% and 68%, respectively, could exhibit days where Tmin-Tdew < 2 °C does not reflect well-watered soil and healthy grass but rather high RH levels (r2 = 0.77 and 0.57, respectively). As this correction methodology was not established considering Tmin-Tdew values smaller than 2 °C, the application scope of this methodology is limited under the above scenarios.

Numerical-experimental approach to identify the effect of relative humidity on the material parameters of a rate-dependent damage model for polyamide 66

This work aims at identifying the behavior of polyamide 66 (PA66) under different Relative Humidity (RH) conditions using a phenomenological model that accounts for viscoelastic and viscoplastic rheology coupled to ductile damage. An experimental approach is designed considering different loading conditions, namely: monotonic at several strain rates, loading–unloading, creep-recovery, and cyclic tests. These experiments are chosen to discriminate the various active mechanisms governing the nonlinear behavior of PA66. The thermodynamic background of the phenomenological model, the evolution laws, and the accompanying RH-dependent material parameters are presented and discussed. Using the experimental findings, an optimization algorithm is adopted to identify the model parameters. The latter are investigated with regard to the relative humidity, leading hence to the development of a model that accounts for the effect of RH on all inelastic mechanisms and ductile damage. Validation through experimental data for RH = 0%, 25%, 50%, 65%, and 80% reveals that the current model captures the effect of RH and yields mechanical responses in good agreement with experimental findings, notably at higher RH levels. The current numerical-experimental framework presents a unified model for a wide range of humidity conditions and provides a better insight into material properties and rate-dependent inelastic mechanisms under humidity exposure, which typical models do not provide. In addition, the present constitutive law is easily adoptable in micromechanics schemes for the study of polymer based composite materials and structures.

Zero Threshold for Water Adsorption on MAPbBr3

Hybrid organic-inorganic perovskites (HOIPs) have shown great promise in a wide range of optoelectronic applications. However, this performance is inhibited by the sensitivity of HOIPs to various environmental factors, particularly high levels of relative humidity. This study uses X-ray photoelectron spectroscopy (XPS)to determine that there is essentially no threshold to water adsorption on the in situ cleaved MAPbBr3 (001) single crystal surface. Using scanning tunneling microscopy (STM), it shows that the initial surface restructuring upon exposure to water vapor occurs in isolated regions, which grow in area with increasing exposure, providing insight into the initial degradation mechanism of HOIPs. The electronic structure evolution of the surface wasalso monitored via ultraviolet photoemission spectroscopy (UPS), evidencing an increased bandgap state density following water vapor exposure, which is attributed to surface defect formation due to lattice swelling. This study will help to inform the surface engineering and designs of future perovskite-based optoelectronic devices.

An Efficient Ambient-Moisture-Driven Wearable Electrical Power Generator.

Existing devices for generating electrical power from water vapor in ambient air require high levels of relative humidity (RH), cannot operate for prolonged periods, and provide insufficient output for most practical applications. Here a heterogeneous moisture-driven electrical power generator (MODEG) is developed in the form of a free-standing bilayer of polyelectrolyte films, one consisting of a hygroscopic matrix of graphene oxide(GO)/polyaniline(PANI) [(GO)PANI] and the other consisting of poly(diallyldimethylammonium chloride)(PDDA)-modified fluorinated Nafion (F-Nafion (PDDA)). One MODEG unit (1 cm2 ) can deliver a stable open-circuit output of 0.9V at 8µA for more than 10h with a matching external load. The device works over a wide range of temperature (-20 to +50 °C) and relative humidity (30% to 95% RH). It is shown that series and parallel combinations of MODEG units can directly supply sufficient power to drive commercial electronic devices such as light bulbs, supercapacitors, circuit boards, and screen displays. The (GO)PANI:F-Nafion (PDDA) hybrid film is embedded in a mask to harvest the energy from exhaled water vapor in human breath under real-life conditions. The device could consistently generate 450-600mV during usual breathing, and provides sufficient power to drive medical devices, wearables, and emergency communication.