Federated learning, as a novel distributed machine learning mode, enables the training of machine learning models on multiple devices while ensuring data privacy. However, the existence of single-point-of-failure bottlenecks, malicious threats, scalability of federated learning implementation, and lack of incentive mechanisms have seriously hindered the development of federated learning technology. In recent years, as a distributed ledger, blockchain has the characteristics of decentralization, tamper-proof, transparency, security, etc., which can solve the issues encountered in the above-mentioned federated learning. Particularly, the integration of federated learning and blockchain leads to a new paradigm, called blockchain-based federated learning (BFL), which has been successfully applied in many application scenarios. This paper aims to provide a comprehensive review of recent efforts on blockchain-based federated learning. More concretely, we propose and design a taxonomy of blockchain-based federated learning models, along with providing a comprehensive summary of the state of the art. Various applications of federated learning based on blockchain are introduced. Finally, we expand on current trends and provide new perspectives pertaining to this new and exciting development in the field.

Efficient solar vapor/steam generation is important for various applications ranging from power generation, cooling, desalination systems to compact and portable devices like drinking water purification and sterilization units. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems and have relatively low efficiency due to bulk heating of the entire liquid volume. Recently, by incorporating novel light harvesting receivers, a new class of solar steam generation systems has emerged with high vapor generation efficiency. They are categorized in two research streams: volumetric and floating solar receivers. In this paper, we review the basic principles of these solar receivers, the mechanism involving from light absorption to the vapor generation, and the associated challenges. We also highlight the two routes to produce high temperature steam using optical and thermal concentration. Finally, we propose a scalable approach to efficiently harvest solar energy using a semi-spectrally selective absorber with near-perfect visible light absorption and low thermal emittance. Our proposed approach represents a new development in thermally concentrated solar distillation systems, which is also cost-effective and easy to fabricate for rapid industrial deployment.

3D printing complex architectures of responsive-hydratable polymers are enabled by stereolithography via photopolymerization. Yet, insufficient crosslinking leads to compromised structural integrity of the photopolymerized samples, which affects the functionality and reliability of hydrogel devices significantly. Here we investigate how curing parameters and ink formulation affect 3D printed PEGDA samples by using a combination of microfabrication, structural characterization, and reactive coarse-grained molecular dynamics simulation. Our findings show that the degree of curing exhibits a graded profile from confocal Raman spectroscopy and submicron pores from atomic force microscopy, both of which are also observed in our molecular simulations. Moreover, with environmental scanning electron microscopy, we probe the microscopic swelling and bending dynamics of 3D printed hydratable PEGDA structures as well as their structural integrity. Our in-depth characterization results reveal how hydrogel elasticity and irreversible densification due to pore formation highly depends on the exposure time, light intensity and the associated degree of crosslinking. This work provides new molecular insights into processing–structure relation in stereolithography 3D printing.

Direct solar vapor generation (SVG) provides a sustainable and eco‐friendly solution to the current global water scarcity challenges. However, existing SVG systems operating under natural sunlight suffer from low water yield and high energy requirement of vaporization. New materials with reduced latent heat of water vaporization are in urgent demand to boost SVG process. Herein, we propose a novel strategy to additively fabricate anisotropic hybrid 3D structure from photocurable thermoresponsive p(NIPAm‐co‐PEGDA) hydrogel on the top of PEGDA foam for SVG. The in‐situ post‐printing synthesis of iron oxide nanoparticles within the p(NIPAm‐co‐PEGDA) hydrogel on the top surface, thus introducing anisotropy, is achieved by adding metallic salt precursor into the printing solution. The as‐fabricated hydrogel composite structure exhibits superior light absorption properties and rapid capillary‐driven water transport through a 3D‐printed microchannel network within the hydrogel. As a result, our SVG device achieves an extraordinary water evaporation rate of 5.12 kg m⁻² h⁻¹ under one sun (1 kW/m²). The intrinsic water activation states, in addition to wettability modulation with temperature increase within p(NIPAm‐co‐PEGDA) hydrogel, plays a critical role in reducing the equivalent vaporization enthalpy and shifting the vaporization to relatively lower temperatures. The proposed hybrid SVG device is feasible, portable, and highly efficient, promising great potential for grand water‐energy nexus challenges. image