This paper reports on a mat-like flexible thermoelectric system (FTES) based on rigid inorganic bulk materials, i.e. Bi–Te compounds. Inorganic bulk materials exhibit higher thermoelectric performance and can create a larger temperature drop due to their considerable height compared with organics and printable inorganics, meaning the FTES can produce an impressive power output. We show that the FTES, wherein both a thermoelectric module and a heat sink are integrated, is flexible enough to be adapted to any irregularly shaped surface. In the FTES, p- and n-type legs composed of a thermoelectric module are placed inside holders, which are connected to one another using flexible wires. Powered by a portable battery, the FTES was used to refrigerate human skin. As a result, a temperature drop of approximately 4 K was experimentally demonstrated, which humans felt as ‘cold’ or ‘very cold’, based on analysis. This indicates the feasibility of using the proposed FTES to control the temperature of the human body, even when using a portable battery. This was also applied to body heat harvesting. The FTES generated approximately 88 µW of power, which is sufficient to operate most wearable and/or implantable sensors. Our analysis based on human thermoregulatory modeling indicates that both refrigeration and power generation capacity can be further enhanced by improving the thermal contact between the FTES and human skin. The FTES shows potential for wearable refrigeration and body heat harvesting.
Searching environmentally friendly and low‐cost catalysts for CO2 reduction is critical for the development of sustainable energy and environmental technologies. In this work, we report a novel heterointerface between graphene and BN nanotubes or nanoribbons as efficient catalysts for CO2 reduction with high activity and selectivity. The active sites are found to be at the C‐N interfaces of graphene‐BN (G‐BN) and their excellent catalytic performance is derived from the surface curvature effect. The density functional theory (DFT) results reveal that the most energy favorable pathway for the formation of CH3OH is * + CO2 → *COOH → *CO → *OCH → *OCH2 → *OCH3 → *CH3OH → * + CH3OH. And the formation of CH4 is through * + CO2 → *COOH → *CO → *OCH → *OCH2 → *OCH3 → *O + CH4 → *OH + CH4 → *H2O + CH4 pathway. Moreover, the calculated results further demonstrate that for the smaller index of G‐BN nanotubes, such as G‐BN (3), the formation of CH3OH product is much easier than the *O intermediate and CH4 molecule due to the lower free energy change. However, for the higher indexed G‐BN nanotubes, after forming *OCH3 intermediate, the generation of *O and CH4 molecule is more feasible, particularly for G‐BN (9), and the calculated limiting potential is only −0.42 V, which is higher than the best Cu‐based materials, like −0.93 V on Cu(111), and −0.74 V on Cu (211). This metal free heterostructure is confirmed to facilitate CO2 conversion with high activity and selectivity, demonstrating a great potential as a new type of catalyst for CO2 reduction.
Favourable band alignment and excellent visible light response are vital for photochemical water splitting. In this work, we have theoretically investigated how ferroelectric polarization and its reversibility in direction can be utilized to modulate the band alignment and optical absorption properties. For this objective, 2D van der Waals heterostructures (HTSs) are constructed by interfacing monolayer MoS2 with ferroelectric In2Se3. We find the switch of polarization direction has dramatically changed the band alignment, thus facilitating different type of reactions. In In2Se3/MoS2/In2Se3 heterostructures, one polarization direction supports hydrogen evolution reaction and another polarization direction can favour oxygen evolution reaction. These can be used to create tuneable photocatalyst materials where water reduction reactions can be selectively controlled by polarization switching. The modulation of band alignment is attributed to the shift of reaction potential caused by spontaneous polarization.Additionally, the formed type-II van der Waals HTSs also significantly improve charge separation and enhance the optical absorption in the visible and infrared regions. Our results pave a way in the design of van der Waals HTSs for water splitting using ferroelectric materials.
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