Photo-thermal energy cycles for thermochromic displays with control of heat output.

A closed-cycle system for light-harvesting, storage, and heat release is important for utilizing and managing renewable energy. However, combining a high-energy, stable photochromic material with a controllable trigger for solid-state heat release remains a great challenge for developing photothermal fuels (PTFs). This paper presents a uniform PTF film fabricated by the assembly of close-packed bisazobenzene (bisAzo) grafted onto reduced graphene oxide (rGO). The assembled rGO-bisAzo template exhibited a high energy density of 131 Wh kg and a long half-life of 37 days owing to inter- or intramolecular H-bonding and steric hindrance. The rGO-bisAzo PTF film released and accumulated heat to realize a maximum temperature difference (DT) of 15 °C and a DT of over 10 °C for 30 min when the temperature difference of the environment was greater than100 °C. Controlling heat release in the solid-state assembly paves the way to develop highly efficient and high-energy PTFs for a multitude of applications.

It is highly challenging to achieve an optically deformable polymer with good controllability, stability, and self-healability for fabricating an optically controlled microrobotics. Here, we present a photo-responsive self-healing supramolecular assembly cross-linked by 3,3',5,5'-azobenzenetetracarboxylic acid (t-Azo) enabling the controllable and stable deformation. The network (PAA-u) of polyacrylic acid (PAA) grafted with 2-ureido-4[1 H]-pyrimidinone (UPy) is formed via multiple intermolecular hydrogen bonds (H-bonds) between UPy and t-Azo moieties. Molecular H-bonds stabilize the cis-isomer, enables stress transfer at the interface, and also contributes to fast healability. The PAA-u/t-Azo assembly shows a green-light-induced bending deformation, which recovers its shape under the irradiation of UV light. On the basis of this controllable and reversible deformation, the PAA-u/t-Azo "hand" realizes reversible light-driven grabbing and releasing of an object by optimizing bending and recovery. The assembly also shows a fast and excellent self-healing performance irradiated by green light during deformation. The multiple-H-bonding-cross-linked assembly with stable deformation and fast self-healability can be used for the development of a multitude of advanced microrobotics.

Nitrogen (N2) fixation at ambient condition by electrochemical N2 reduction reaction (NRR) is energy‐efficient and eco‐friendly as compared to the traditional Harber–Bosch process, but it is extremely challenging. Development and design of high‐performance NRR electrocatalysts are indispensable to achieve the goal. In this work, a strongly coupled hybrid of nano‐Fe3O4 with reduced graphene oxide (rGO) is synthesized via an in situ redox hydrothermal approach, and the synthesized Fe3O4@rGO hybrid has excellent activity, selectivity, and stability as an NRR catalyst. The NH3 yield rate of 28.01 μg h‐1 mg‐1 at −0.3 V and the Faradaic efficiency (FE) of 19.12% at −0.1 V are obtained in 0.1 M Na2SO4 solutions at ambient conditions. The superior NRR performance is attributed to the chemical coupling effect between rGO and nano‐Fe3O4 particles, which leads to the enhancement of the binding affinity to N2 molecules, improvement of the conductivity, and lowering the free energy of reaction for the limiting reaction step. This work provides a facile route in fabricating hybrid NRR catalysts with superior performance and shed lights on the reaction mechanism with theoretical mechanistic calculations.

Invited for this month's cover is the group of Wei Feng at Tianjin University. The image shows that photo‐thermal fuels (PTFs) using a bisazobenzene–graphene assembly can be developed for utilizing solar thermal energy in the space. The Full Paper itself is available at 10.1002/cssc.201601551.