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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. 

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. 

Abstract Smart windows have the potential to respond dynamically and passively to external stimuli, controlling the amount of light passing through the window. When a smart window switches from a clear to a translucent state, energy flow through the window is partially attenuated, allowing a room to cool down passively, thereby reducing the energy and fossil fuel consumption for air conditioning. The smart window demonstrated here consists of a thermoresponsive liquid consisting of Tergitol 15‐S‐7, which can dynamically and passively switch the window's transmittance when a temperature of 39 °C is reached. It is also demonstrated how the transition temperature can be lowered by adding salts. Outdoor experiments in realistic environments show that the temperature of a model house built with a thermo‐responsive window can achieve an indoor temperature of 7 °C less than a control house with an ordinary window. This study quantifies the energy savings possible using such windows at the building scale for cooling and heating in different climates and times of the year.