Solar-driven water splitting offers a direct path to green hydrogen by using sunlight to split water into hydrogen and oxygen, enabling flexible energy storage and hydrogen fuel production. Yet, turning lab-scale demonstrations into widespread deployment requires overcoming intertwined fundamental and engineering challenges. This Voices piece gathers researchers from around the world who work on photocatalytic, photoelectrochemical, and biophotoelectrochemical water splitting to discuss bottlenecks, promising strategies, and the tools most helpful for advancing solar fuels production. They address design principles for materials and devices, emerging configurations and benchmarking concepts, pathways to commercialization, and how related catalytic processes and adjacent fields can guide sustainable hydrogen evolution. What becomes clear is that achieving scalable solar-driven hydrogen production will require integrated, multi-disciplinary efforts that bridge responsible discovery and deployment.

Two-dimensional (2D) materials hold significant promise for next-generation nanoelectronics while introducing critical thermal management challenges. The extreme thinness, anisotropic heat transport, and unique interfacial coupling make the thermal design principles of 2D materials-based electronics fundamentally different from that of bulk systems. In this Perspective, we discuss exciting opportunities that leverage recent advances in thermal science to unlock unprecedented thermal management capabilities, thereby providing new insights into the design of 2D materials-based electronics. We first provide an overview of key thermophysical properties of 2D materials that govern thermal management performance, including in-plane thermal conductivity, interfacial thermal conductance, and thermal expansion coefficient. Then, we not only highlight important physical phenomena distinct from bulk materials but more notably illustrate how the interplay among these thermophysical properties ultimately dictates the unique characteristics of heat dissipation and thermomechanical stress in 2D materials-based electronic devices. With both material- and device-level insights, we identify key thermal bottlenecks in existing 2D materials-based electronic devices and present a fully quantitative roadmap toward an electrical and thermal co-design strategy for substantially improved thermal management. Bridging thermal innovations to the device design, we envision this Perspective can foster next-generation thermal management technologies for reliable 2D materials-based electronics.

Atmospheric water harvesting helps unlock clean water access wherever it is needed but practical deployment remains limited by low water productivity. A modular, field-portable, and solar-powered platform now brings litre-scale water production across diverse environments.

Photosynthetic biomanufacturing offers a sustainable route to generate valuable bioproducts by harnessing microorganisms such as algae to convert sunlight and carbon dioxide into biomass. A major barrier to efficient production is that light penetrates poorly into dense algal cultures, restricting photosynthesis to a thin surface layer and severely limiting the solar energy that can be utilized for algal growth and biomass production. Here, we present a material-based strategy to overcome this fundamental bottleneck by deploying bulk-scattering, index-matched optical fibers that redistribute sunlight uniformly throughout the culture volume. These fibers are made from amorphous hydrogels with a refractive index closely matched to that of algal media and contain scattering nanoparticles that redirect light to achieve volumetric illumination. When integrated into solar-powered algal systems, the fibers enable dense and sustained algal growth at 0.8 to 1.4 g L-1 over 2 mo of semicontinuous outdoor cultivation, resulting in volumetric biomass productivity of 0.15 g L-1 day-1 and photosynthetic efficiency of 1.4%, significantly higher compared to algal systems without fibers. This study demonstrates the transformative potential of optical modulation to the long-standing low productivity in dense algal culture, providing a scalable, sustainable, and efficient pathway for solar-driven biomanufacturing.

Molecular transport through polymer networks, including hydrogels and biological matrices, underpins many applications ranging from water filtration and gas separation to drug delivery and cell culture. Conventional strategies for regulating transport in polymer networks primarily focus on tuning molecular diffusion through network mesh size and polymer chemistry, whereas convection is often considered negligible because nanoscale-mesh networks typically exhibit low fluid permeability. Although hydraulic pressure is a well-established driving force for convection in porous media, extending pressure-driven convection to non-porous polymer networks has remained fundamentally challenging because they can undergo substantial deformation or fracture under pressure gradients. Here, we demonstrate that hydraulic pressure applied across mechanically tough and grid-supported hydrogels enables robust and tunable solute transport while maintaining structural integrity. The characteristic transport time can be experimentally modulated by up to 65-fold, consistent with a coupled diffusion-convection model. Beyond tuning transport kinetics, applied pressure enhances size- and charge-dependent transport selectivity by up to 5.4-fold compared to pressure-free conditions. As a proof of concept, we demonstrate pressure-programmed antimicrobial delivery that dynamically controls doxorubicin transport while blocking bacterial penetration. These findings identify pressure-regulated convection as an underexplored mechanism for controlling transport in polymer networks.

Nucleation is classically treated as a local process, yet whether coupling between neighboring sites governs activation and stability remains unexplored. Here we show bubble nucleation is fundamentally collective: sites separated by the hydrodynamic-boundary-layer scale activate more readily and resist deactivation under changing thermal loads, consistent with a non-local hydrodynamic shielding mechanism, whereby neighboring bubbles slow the intervening flow, suppress convective heat removal, and stabilize vapor embryos. Using surfaces with two independently tunable length scales, we isolate this near-wall coupling from a second collective process, coalescence between departing bubble clusters, which transitions through isolated, promotive, and excessive regimes as the departure diameter grows with heat flux. The dominant length scale thus shifts with operating conditions, from boundary-layer coupling near activation to departure-scale coupling once nucleation is established. These results establish a scale-dependent framework for collective nucleation and departure, broadly related to phase change processes on structured surfaces.

Thermally localized solar evaporation has been recognized as an efficient and suitable pathway for desalination and brine treatment. However, the annoying salt crystallization inside the porous evaporator poses challenges in hypersaline brine evaporation. Here, we propose that the salt crystals can serve as an ideal structure for evaporation with proper manipulations. Taking advantage of the self-amplifying salt creeping and efflorescence effects, the salt crystals self-assemble to form a hierarchical porous salt evaporator (HPSE), enabling passive liquid supply and efficient evaporation. With a low-cost, solar-powered device based on HPSE, we achieve stable evaporation and crystallization when treating the hypersaline brine with 27.3 wt% salinity under one-sun illumination, resulting in a high evaporation rate of 18.78 kg m-2 h-1. This work bridges the important knowledge gap between the fundamental salt crystallization and brine treatment, paving a path toward sustainable water economy.

Droplets are prone to adhere or "pin" on solid surfaces which contain unavoidable micro- and nanoscale surface defects formed through chemical and topographical heterogeneity. To initiate droplet motion, potential energy gradients, surface energy gradients, or external energy input are needed. Here, in contrast to established wisdom, we show that properly designed surface heterogeneity can promote microdroplet self-transport without any external force or anisotropy. In the presence of topological defects, microdroplets can take advantage of contact line pinning to generate contact line and corresponding contact angle asymmetry, leading to spontaneous motion over distances 10-20 times larger than the droplet radius. The outcomes of this work present an alternative pathway for taking advantage of intrinsic surface heterogeneity to achieve droplet mobility in a range of applications, where passive droplet motion is desired.

Scaling up water electrolysis to high current densities inevitably induces massive gas evolution at electrode interfaces, posing critical challenges to interfacial transport and system stability. While individual bubble dynamics have been extensively studied, the collective behaviors and critical transitions of densely populated bubbles under extreme conditions remain poorly understood. Here we present a synchronized acoustic–visual framework for characterizing hydrogen bubble evolution during alkaline electrolysis, enabling the segmentation of the polarization curve into four distinct regimes: nucleate whisper, resonant growth, cascade detachment, and turbulent film. This regime map constitutes an electrolytic gas evolution curve, an electrochemical analogue of the classical boiling curve. We identify a critical current density at which interfacial gas accumulation triggers a sharp performance inflection. Near this threshold, bubble dynamics exhibit scale-free acoustic energy distributions and clustered detachment behavior, signaling the emergence of self-organized criticality. Our findings establish a mechanistic foundation linking bubble evolution modes, dynamic acoustic fingerprints, and mass transport transitions under extreme electrolysis conditions, offering a new paradigm for monitoring, diagnosing, and optimizing high-rate gas-evolving electrochemical systems.

Salt creeping, the precipitation of salt crystals ahead of the liquid front of an evaporating salt solution, poses severe challenges to agriculture, buildings and structures, maritime field, and art conservation while holding significant promise for wastewater treatment and mineral extraction. Despite their critical role, insights into the key mechanisms of salt creeping remain elusive. Here, we leverage in situ X-ray microscopy to unravel the onset of salt creeping at a single-crystal level. Notably, we directly image the first salt crystal pinned on the solid-liquid interface, which penetrates the liquid meniscus and initiates a cascading crystallization process. New salt crystals precipitate from the extended meniscus created by the initial salt crystal. Combining X-ray imaging with thermodynamic analysis, we demonstrate that the formation of the first pinned crystal is associated with a critical contact angle of the liquid meniscus. This work elucidates the microscopic origin of salt creeping, shedding light on the effective manipulation of salt crystallization for various applications.

Solar-powered water electrolysis holds significant promise for the mass production of green hydrogen. However, the substantial water consumption associated with electrolysis not only increases the cost of green hydrogen but also raises critical concerns about accelerating water scarcity. Although seawater can serve as an infinite water supply for green hydrogen production, its complex composition poses substantial challenges to efficient and reliable electrolysis. Here, we demonstrate a high-efficiency solar-powered green hydrogen production from seawater. Our approach takes advantage of the full-spectrum utilization of solar energy. Photovoltaic electricity is used to drive the electrolysis, whereas the waste heat from solar cells is harnessed to produce clean water through seawater distillation. With natural sunlight and real seawater as the sole inputs, we experimentally demonstrate a 12.6% solar-to-hydrogen conversion efficiency and a 35.9 L m-2 h-1 production rate of green hydrogen under one-sun illumination, where additional 1.2 L m-2 h-1 clean water is obtained as a byproduct. By reducing reliance on clean water and electricity supplies, this work provides a fully sustainable strategy to access green hydrogen with favorable energy efficiency and technoeconomic feasibility.

Gas bubble evolution plays a pivotal role in water electrolysis. Electrochemical gas evolution reactions operating at high current densities represent a promising future trend for improving efficiency. However, the lack of reliable bubble detection methods in electrochemical gas evolution systems, as well as the limited understanding of bubble behavior at different current levels, hinder a comprehensive understanding of the actual bubble dynamics under various voltage and current conditions. To address this challenge, a novel methodology that utilizes acoustic emission signals is proposed to evaluate bubble behavior in the electrolyzer. The dynamic variations in the amplitude and frequency of the acoustic emissions can be correlated with the different stages of bubble evolution. By combining this acoustic technique with high-speed optical imaging, the relationship between the acoustic signal variations and the characteristics of bubble release under different voltage and current levels can be unvealed. Furthermore, clustering algorithms from machine learning are employed to determine bubble acoustic characteristics under various conditions based on the acoustic variations, which allows for redefining the polarization curve. These findings significantly enhance the understanding of the actual bubble behavior under different voltage and current intensities, going beyond the traditional pool boiling curve-based approach. The results demonstrate that acoustic emission can serve as an effective and non-intrusive tool for monitoring bubble formation in gas evolution reactions, making it particularly valuable for applications in non-transparent electrolyzer cells. This facile operating approach offers a new perspective for studying and optimizing electrochemical gas evolution processes.

Global warming intensifies heat stress, posing substantial challenges to cultivated plants and agricultural yield production. The high solar absorptance of soil results in elevated temperatures, pushing plants beyond their ideal growth range. Additionally, this rise in soil temperature accelerates soil moisture evaporation, further aggravating existing water scarcity issues. Common cooling solutions tends to consume significant amounts of water or offer limited cooling capacities. In response, a radiative cooling and moisturizing film composed of biodegradable ethyl-cellulose was developed. With a solar reflectance of 97% and a thermal emissivity of 0.93, this film provides efficient zero-energy cooling for soil surfaces. Field tests have demonstrated that compared to commercial cooling mulch, the radiative cooling film significantly reduces soil temperature and moisture evaporation by 50% and 60%, respectively. Furthermore, it boosts plant growth by 30% by moderating leaf temperatures and augmenting the exposure to reflected sunlight, crucial for photosynthesis on hot days. Global heat-water simulations reveal that the film increases soil moisture preservation by over 80% and alleviates agricultural water scarcity by over 60% in arid regions during hot seasons. This work offers a practical and sustainable solution to mitigate heat stress and promote resilient cultivation practices in the context of global warming.

The presence of gas bubbles in electrochemical systems, such as water-splitting, significantly increases overpotential and diminishes energy efficiency. High-fidelity simulation holds significant promise to gain mechanistic understanding of bubble dynamics and guide high-performance electrolytic cell design. However, the extreme length scales involved into electrochemical gas evolving systems, from sub-nanometer dictated by the electrical double layer (EDL) to a few centimeters featured by the electrolytic cell, have posed a huge challenge to enable sufficient numerical accuracy and superior computational efficiency. As a result, state-of-the-art numerical approaches either can only simulate a nanoscale computational domain or neglect the electrochemical kinetics within the EDL, impeding an in-depth understanding of how bubbles could intervene with the electrochemical process. In this work, we demonstrate a full-field simulation approach of electrochemical gas evolving reactions that can capture the electrochemical kinetics of the EDL in a centimeter-scale electrolytical cell with the presence of micro-to-millimeter scale bubbles. To resolve all characteristic length scales, the EDL is geometrically decoupled from the electrolytical cell but physically coupled with the bulk electrolyte and gas bubble through a quasi-1D treatment. As a result, the Nernst-Planck-Poisson-Boltzmann model can be rigorously solved in both the EDL and the rest of the electrolytical cell with highly affordable computational cost. Taking hydrogen evolution reaction as an example, we validated our approach by comparing with a variety of existing numerical and experimental results. For the first time, the impact of bubbles on the increase of overpotential observed in experiments can be quantitatively confirmed through numerical simulation. More notably, compared to state-of-the-art high-fidelity simulations, our approach exhibits a remarkable computational efficiency, which reduced the computational time by a factor of 100,000. This work provides a viable solution to simulate electrochemical gas evolving reactions with highly desirable numerical accuracy and unprecedented computational efficiency, which can serve as an effective tool to understand bubble dynamics and guide the design of next-generation electrolytical cells.

Sorption-based atmospheric water harvesting (SAWH) offers a sustainable strategy to address the global freshwater shortage. However, obtaining sorbents with excellent performance over a wide relative humidity (RH) range and devices with fully autonomous water production remains challenging. Herein, magnesium chloride (MgCl2) is innovatively converted into super hygroscopic magnesium complexes(MC), which can effectively solve the problems of salt deliquescence and agglomeration. The MC are then integrated with photothermal aerogels composed of sodium alginate and carbon nanotubes (SA/CNTs) to form composite aerogels, which showed high water uptake over a wide RH range, reaching 5.43 and 0.27 kg kg-1 at 95% and 20% RH, respectively. The hierarchical porous structure enables the as-prepared SA/CNTs/MC to exhibit rapid absorption/desorption kinetics with 12 cycles per day at 70% RH, equivalent to a water yield of 10.0 L kg-1 day-1. To further realize continuous and practical freshwater production, a fully solar-driven autonomous atmospheric water generator is designed and constructed with two SA/CNTs/MC-based absorption layers, which can alternately conduct the water absorption/desorption process without any other energy consumption. The design provides a promising approach to achieving autonomous, high-performance, and scalable SAWH.

The atmosphere contains 13,000 trillion litres of water, and it is a natural resource available anywhere. Sorption-based atmospheric water harvesting (SAWH) is capable of extracting water vapour using sorbent materials across a broad spectrum of relative humidity, opening new avenues to address water scarcity faced by two-thirds of the population of the world. Although substantial progress has been made, there is still a considerable barrier between fundamental research and real-world applications. In this Review, we provide a multiscale perspective for SAWH technologies that can fill existing knowledge gaps across multiple length scales. First, we elucidate water sorption mechanisms at the molecular level, approaches to understanding sorbent materials, and water transport phenomena. With microscopic insights, we bridge materials innovations to device realization, discuss strategies to enhance device-level sorption kinetics and heat transfer performance, and show that a multiscale design and optimization strategy can lead to a new opportunity space towards system thermodynamic limits. Finally, we provide an outlook for the technoeconomic, social and environmental impact of large-scale SAWH as a global water technology. By bridging materials to devices, we envision that this multiscale perspective can guide next-generation SAWH technologies and facilitate a broader impact on society and the environment. Harvesting freshwater from the air using water sorption materials is an innovative strategy to address water scarcity. This Review offers a multiscale perspective to design the next generation of sorption-based atmospheric water harvesting technology by bridging materials innovations to device realization and provides practical guidelines to understand its real-world impact.

Bubbles play a ubiquitous role in electrochemical gas evolution reactions. However, a mechanistic understanding of how bubbles affect the energy efficiency of electrochemical processes remains limited to date, impeding effective approaches to further boost the performance of gas evolution systems. From a perspective of the analogy between heat and mass transfer, bubbles in electrochemical gas evolution reactions exhibit highly similar dynamic behaviors to them in the liquid-vapor phase change. Recent developments of liquid-vapor phase change systems have substantially advanced the fundamental knowledge of bubbles, leading to unprecedented enhancement of heat transfer performance. In this Review, we aim to elucidate a promising opportunity of understanding bubble dynamics in electrochemical gas evolution reactions through a lens of phase change heat transfer. We first provide a background about key parallels between electrochemical gas evolution reactions and phase change heat transfer. Then, we discuss bubble dynamics in gas evolution systems across multiple length scales, with an emphasis on exciting research problems inspired by new insights gained from liquid-vapor phase change systems. Lastly, we review advances in engineered surfaces for manipulating bubbles to enhance heat and mass transfer, providing an outlook on the design of high-performance gas evolving electrodes.

Adsorption systems promise to address energy storage, water harvesting, and carbon capture, among other applications in energy and sustainability. Improving the kinetics of the sorbent layer is essential to enable substantial enhancement in the performance of such systems, but challenges remain owing to the highly tortuous and random distribution of adsorbents. Here, we present a boiling -assisted channel-templating (BACT) coating method to enhance the kinetics of sorbent layers. Driven by boiling -induced vapor flow, randomly distributed adsorbents become well aligned, approaching the theoretical minimum tortuosity of porous structures. Using water adsorption in zeolite-coated copper foam, we demonstrate 2x improvement in effective diffusivity. We develop design guidelines to control the porous structure. For AQSOA-Z02 coating, the BACT method was able to reduce tortuosity to 1.09. We show the impact of BACT on adsorptive systems where cyclability can be improved by approximate to 1.7x compared with state-of-the-art coatings. This work demonstrates a simple, low-cost, and scalable approach to enhance sorption kinetics.

Recent advances in multistage solar distillation are promising for the sustainable supply of freshwater. However, significant performance degradation due to salt accumulation has posed a challenge for both long-term reliability of solar desalination and efficient treatment of hypersaline discharge. Here, inspired by a natural phenomenon, thermohaline convection, we demonstrate a solar-powered multi-stage membrane distillation with extreme salt-resisting perfor-mance. Using a confined saline layer as an evaporator, we initiate strong thermohaline convection to mitigate salt accumulation and enhance heat transfer. With a ten-stage device, we achieve re-cord-high solar-to-water efficiencies of 322%-121% in the salinity range of 0-20 wt % under one-sun illumination. More importantly, we demonstrate an extreme resistance to salt accumulation with 1 80-h continuous desalination of 20 wt % concentrated seawater. With high freshwater production and extreme salt endurance, our device significantly reduces the water production cost, paving a pathway toward the practical adoption of passive solar desalination for sustainable water economy.