Roadmap on energy harvesting materials

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere

Crystallinity-Dependent Thermoelectric Properties of a Two-Dimensional Coordination Polymer: Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2

The evaluation of thermoelectric properties has recently become a standard method for revealing the electronic properties of conducting polymers. Herein we report on the thermoelectric properties of a two-dimensional coordination polymer pellets. The pellets of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, which has recently been developed, show n-type thermoelectric transport, dependent on crystallinity. The present results provide systematic feedback to the guideline for high-performance molecular thermoelectric materials

Crystallinity-Dependent Thermoelectric Properties of a Two-Dimensional Coordination Polymer: Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2

The evaluation of thermoelectric properties has recently become a standard method for revealing the electronic properties of conducting polymers. Herein we report on the thermoelectric properties of a two-dimensional coordination polymer pellets. The pellets of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, which has recently been developed, show n-type thermoelectric transport, dependent on crystallinity. The present results provide systematic feedback to the guideline for high-performance molecular thermoelectric materials

Thickness-dependent thermoelectric power factor of polymer-functionalized semiconducting carbon nanotube thin films

The effects of polymer structures on the thermoelectric properties of polymer-wrapped semiconducting carbon nanotubes have yet to be clarified for elucidating intrinsic transport properties. We systematically investigate thickness dependence of thermoelectric transport in thin films containing networks of conjugated polymer-wrapped semiconducting carbon nanotubes. Well-controlled doping experiments suggest that the doping homogeneity and then in-plane electrical conductivity significantly depend on film thickness and polymer species. This understanding leads to achieving thermoelectric power factors as high as 412 μW m−1 K−2 in thin carbon nanotube films. This work presents a standard platform for investigating the thermoelectric properties of nanotubes

Chiral Monolayer-Protected Bimetallic Au–Ag Nanoclusters: Alloying Effect on Their Electronic Structure and Chiroptical Activity

Chiral glutathione (GSH)-protected bimetallic Au–Ag nanoclusters (AuAg­(SG)) are synthesized by the reduction of mixtures of Au and Ag salts at the feed mole ratio of Au/Ag = 3/1 in the presence of GSH and isolated by gel electrophoretic separation, yielding a family of magic-numbered bimetallic Au–Ag nanoclusters. The PAGE pattern similarity between Au­(SG) and AuAg­(SG) as well as the analyses based on small-angle X-ray scattering and X-ray photoelectron spectroscopy (XPS) allow comparisons of their chemical compositions for each family of nanoclusters, and the fractioned nanocluster compounds (three samples) are identified as Au_12.2Ag_2.8(SG)₁₃, Au_14.4Ag_3.6(SG)₁₄, and Au_17.6Ag_7.4(SG)₁₈. The XPS study also suggests that (i) incorporation of Ag heteroatoms into smaller-sized Au nanoclusters is less favorable and (ii) Ag heteroatoms preferentially occupy sites on the cluster’s core (including the core-surface and center) rather than the peripheral semiring shell. Optical spectroscopy shows that the electronic structures of Au nanoclusters are significantly modulated by incorporation of Ag atoms. Interestingly, the bimetallic Au–Ag nanocluster compounds exhibit weaker circular dichroism (CD) responses than those of the corresponding Au counterparts. Such a decrease in chiroptical responses can be explained in terms of the increased geometrical isomers that are formed by statistical distribution of Ag heteroatoms in the nanocluster because an increased number of possible configurations is expected to give the average in the CD response with positive and negative bands of different optical isomers

Dual Transient Bleaching of Au/PbS Hybrid Core/Shell Nanoparticles

We examined the optical response of hybrid Au/PbS core/shell nanoparticles (NPs) using transient absorption spectroscopy. Finite-difference time-domain (FDTD) calculations and transient absorption measurements show that Au/PbS NPs have unique two extinction peaks: the peak at the longer wavelength (∼700 nm) is originated from the plasmon, and that at the shorter wavelength (550 nm) is from the local maximum of the refractive index of PbS. The transient absorption dynamics of Au/PbS NPs excited at 400 nm have clear oscillation behavior, which is assigned to the breathing mode of whole particle. We observed a weak excitation-wavelength dependence of the plasmon band. The time constant of electron–phonon coupling of Au/PbS NPs was obtained by changing the excitation intensity. We show that spectral properties of Au/PbS NPs are strongly altered by the hybrid formations, while their dynamics differ only minimally compared with those of Au NPs

Simple Salt-Coordinated n-Type Nanocarbon Materials Stable in Air

After more than three decades of molecular and carbon-based electronics, the creation of air- and thermally stable n-type materials remains a challenge in the development of future p/n junction devices such as solar cells and thermoelectric modules. Here a series of ordinary salts are reported such as sodium chloride (NaCl), sodium hydroxide (NaOH), and potassium hydroxide (KOH) with crown ethers as new doping reagents for converting single-walled carbon nanotubes to stable n-type materials. Thermoelectric analyses reveal that these new n-type single-walled carbon nanotubes display remarkable air stability even at 100 °C for more than 1 month. Their thermoelectric properties with a dimensionless figure-of-merit (ZT) of 0.1 make these new n-type single-walled carbon nanotubes a most promising candidate for future n-type carbon-based thermoelectric materials.Grant-in-Aid for Young Scientists (B) of Japan Society for the Promotion of Science. Grant Number: 2679001