• Energy Research

Illustration of protein-based MEG generating electricity by absorbing water from moisture.

Product selectivity in multielectron electrocatalytic reactions is crucial to energy conversion efficiency and chemical production. However, a present practical drawback is the limited understanding of actual catalytic active sites. Here, using as a prototype single-atom catalysts (SACs) in acidic oxygen reduction reaction (ORR), we report the structure-property relationship of catalysts and show for the first time that molecular-level local structure, including first and second coordination spheres (CSs), rather than individual active atoms, synergistically determines the electrocatalytic response. ORR selectivity on Co-SACs can be tailored from a four-electron to a two-electron pathway by modifying first (N or/and O coordination) and second (C-O-C groups) CSs. Using combined theoretical predictions and experiments, including X-ray absorption fine structure analyses and in situ infrared spectroscopy, we confirm that the unique selectivity change originates from the structure-dependent shift of active sites from the center Co atom to the O-adjacent C atom. We show this optimizes the electronic structure and *OOH adsorption behavior on active sites to give the present "best" activity and selectivity of >95% for acidic H2O2 electrosynthesis.

Abstract Conversion and utilization of solar energy is one of the most important strategies being proposed to mitigate the foreshadowed global energy crisis and environmental issues. Amongst the various solar energy conversion pathways, solar-thermal energy conversion is the most straightforward and efficient. Photothermal materials form the key platform for efficient light-to-heat conversion. The generated heat can be utilized to drive steam generation, which has recently attracted widespread and intense research interests due to its great potential to be a cost-effective and environmentally friendly technique for clean-water production. In recent years, extensive efforts have been devoted to improving the efficiency of solar steam generation. The exploration of photothermal materials with extremely high light-to-heat conversion efficiency as well as innovative evaporation configurations paved the way for eminent practical applications. In this article, the photothermal effect of different categories of light absorbing materials is reviewed and discussed. The applications of a series of representative photothermal materials for solar-steam generation are introduced and summarized in detail to reflect the state-of-the-art for solar evaporation. Finally, a brief discussion of the future research perspectives in this field are proposed.

Abstract Interfacial solar steam generation offers a sustainable and affordable technology for seawater desalination and water treatment. During solar steam generation the temperature of the solar evaporation surface is generally higher than the bulk water, which results in energy loss to the bulk water by heat conduction. While many strategies have been developed to minimize and/or eliminate the conductive heat loss, this study focuses on completely reversing conductive heat loss and turning it into an energy extraction from the bulk water to enhance the evaporation during solar steam generation. This was achieved by introducing a certain area of cold evaporation surface between the solar evaporation surface and the bulk water, which led to the conductive heat loss from the solar evaporation surface being completely absorbed and consumed by the cold evaporation surface before reaching the bulk water. Meanwhile, due to its lower surface temperature, the cold evaporation was also able to extract energy from the bulk water, turning the heat conduction loss from the evaporator to the bulk water into the energy harvest from the bulk water. When the surface area of the cold evaporation surface was increased to a certain point (50.3 cm2 in this work), heat flow was reversed, and energy was extracted from the bulk water by the evaporator to enhance solar evaporation. Theoretical simulations agreed well with the experimental results. In addition, as parasitic effects, the cold evaporation surface was also able to gain energy from the ambient air and lower the temperature of the solar evaporation surface, reducing both radiation and convection energy loss. As a result, the evaporation rate and the light-to-vapor energy efficiency of the evaporator were far beyond the theoretical limits, confirming that this strategy has great potential for further practical applications.

The conversion of solar energy into heat for solar steam generation is significant for energy saving and clean water supply. Recent advances in the design and application of photothermal‐based water‐evaporation systems have attracted intense research interest. However, it is imperative to develop a low‐cost and scalable photothermal system with further improved energy conversion efficiency to meet the demand for real‐world applications. Inspired by the natural transpiration process of plants, a wood‐polydopamine‐based photothermal material is developed for solar‐steam generation. Both the wood and polydopamine (PDA) derived from natural products are cost‐effective, biodegradable, and environmentally friendly. The wood–PDA system evaporates thin water film right above the bulk water surface, leading to extremely high efficiencies. Solar steam can be generated only 5 s after light irradiation. The solar‐steam generation efficiency reaches 87% under 1.0 sun. More significantly, an explosive evaporation which bypasses the phase change from liquid to gas is observed on the wood surface under irradiation of more‐intense light. This yields a solar‐steam generation efficiency (calculated by the classic equation) beyond 100% (e.g., 135% under 3.5 sun). It is envisioned that this strategy can be readily applied in practical solar‐evaporation applications due to its simplicity, low cost, and high efficiency.

Interfacial solar water evaporation is a reliable way to accelerate water evaporation and contaminant remediation. Embracing the recent advance in photothermal technology, a functional sponge was prepared by coating a sodium alginate (SA) impregnated sponge with a surface layer of reduced graphene oxide (rGO) to act as a photothermal conversion medium and then subsequently evaluated for its ability to enhance Pb extraction from contaminated soil driven by interfacial solar evaporation. The SA loaded sponge had a Pb adsorption capacity of 107.4 mg g−1. Coating the top surface of the SA sponge with rGO increased water evaporation performance to 1.81 kg m−2 h−1 in soil media under one sun illumination and with a wind velocity of 2 m s−1. Over 12 continuous days of indoor evaporation testing, the Pb extraction efficiency was increased by 22.0% under 1 sun illumination relative to that observed without illumination. Subsequently, Pb extraction was further improved by 48.9% under outdoor evaporation conditions compared to indoor conditions. Overall, this initial work shows the significant potential of interfacial solar evaporation technologies for Pb contaminated soil remediation, which should also be applicable to a variety of other environmental contaminants.

Because of depleting fossil-fuel reserves, together with the impacts of climate change, alternative eco-friendly production of high-value chemicals and renewables is needed. Biomass feedstock is of particular research interest. 5-Hydroxymethylfural (HMF) is a versatile precursor that can be converted to high-value chemicals via electrolysis. Reduction generates precursors for ethers, ketones, polyurethanes, polyesters, and polyethers, e.g., 2,5-dihydroxymethylfuran (DHMF) and 2,5-dimethyletrahydrofuran (DHMTHF), together with high-energy-density premium biofuels, e.g., 2,5-dimethylfuran (DMF), 2,5-hexanedione (HD) and 5,5?-bis(hydroxymethyl) hydrofuroin (BHH). Oxidation HMF yields valuable chemical products, including 2,5-diformyl furan (DFF), 5-hydroxymethyl-2-furan carboxylic acid (HMFCA), 2,5-furan dicarboxylic acid (FDCA), and maleic acid (MA) that are precursors/intermediates for the polymer industry and chemical/pharmaceutical production(s). In this review, we 1) report a comparative summary of the electrocatalytic refinery of HMF, both electro-oxidation and electroreduction pathways, 2) appraise advances in HMF electroreduction reaction (HRR) and HMF electro-oxidation reaction (HOR), 3) assess reaction pathways and mechanisms, 4) establish a design for electrocatalysts including selection of metal materials, design of the geometric structure, and electronic structural modifications to boost HRR and HOR activity and selectivity, 5) evaluate the impact of reaction parameters including pH, electrolyte composition, applied potential, and initial substrate concentration on HRR and HOR, and 6) provide a prospect on future electrochemical refinement of HMF. We conclude that an improved understanding of reaction conditions is needed to practically boost selectivity and activity for the electrochemical refinement of HMF. Findings will benefit in design for electrochemistry and eco-friendly chemistry in generating fine chemicals and, therefore, are of interest to researchers and manufacturers. © 2023 American ...

Interfacial solar-steam generation is a promising and cost-effective technology for both desalination and wastewater treatment. This process uses a photothermal evaporator to absorb sunlight and convert it into heat for water evaporation. However solar-steam generation can be somewhat inefficient due to energy losses via conduction, convection and radiation. Thus, efficient energy management is crucial for optimizing the performance of solar-steam generation. Here, via elaborate design of the configuration of photothermal materials, as well as warm and cold evaporation surfaces, performance in solar evaporation was significantly enhanced. This was achieved via a simultaneous reduction in energy loss with a net increase in energy gain from the environment, and recycling of the latent heat released from vapor condensation, diffusive reflectance, thermal radiation and convection from the evaporation surface. Overall, by using the new strategy, an evaporation rate of 2.94 kg m-2 h-1, with a corresponding energy efficiency of solar-steam generation beyond theoretical limit was achieved.