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Barocaloric cooling, that is, lowering the temperature of a material under pressure action, is an attractive solid‐state effect that can potentially compete with volatile gas‐based cooling. To observe the barocaloric effect (BCE), it is necessary for materials to have high‐entropy, low‐hysteretic phase transitions with a large volume change between phases. Here details on a new FeII complex [Fe(L)(NCS)2], L = N1,N3‐bis((1‐propyl‐1H‐1,2,3‐triazol‐4‐yl)methylene)‐2,2‐dimethylpropane‐1,3‐diamine) possessing spin crossover (SCO) behavior near room temperature with large entropy and volume change are reported, which provides high sensitivity to external pressure. The observed BCE effect, characterized using variable pressure calorimetry, powder X‐ray diffraction, UV–vis, IR, and Raman spectroscopy, shows a colossal isothermal entropy change of >100 J kg−1 K−1 and a reversible adiabatic temperature change of ≈16 K at a pressure of 1 kbar, demonstrating a high refrigerant efficiency compared to other solid‐state materials. These results stimulate further investigations of SCO materials as barocaloric refrigerants, which depend on the proper design of their constituent organic ligands. [ABSTRACT FROM AUTHOR]

As one of the most likely alternatives to traditional vapor compression refrigeration technology, solid refrigeration technology based on the barocaloric effect (BCE) has attracted extensive attention in recent years. Spin-crossover (SCO) compounds are considered suitable for working at low driving pressures due to high-pressure sensitivity and small hysteresis width. However, the entropy change (ΔSSCO) of the SCO compound is smaller than that of other excellent barocaloric materials (plastic crystals and two-dimensional perovskites). Here, we report the BCE of the SCO compound {Fe(pz)2(BH3CN)2} (pz = pyrazine) with a smaller molar mass and a third source of entropy change besides electron and vibrational entropy changes. Compound {Fe(pz)2(BH3CN)2} exhibits high pressure sensitivity ( d T 1 / 2 d P = 20.2 K kbar−1) as well as entropy change (Δ S SCO = 202 J kg−1 K−1). The maximum values of reversible isothermal entropy change (ΔSit,rev,max) and adiabatic temperature change (ΔTad,rev,max) at 1 kbar are only 103 J kg−1 K−1 and ∼0 K, respectively, due to the hysteresis behavior. However, at sufficiently high driving pressures, ΔSit,rev,max exceeds 200 J kg−1 K−1, and ΔTad,rev,max can reach ∼47 K, which exceeds all SCO compounds reported in BCE studies and is comparable to some plastic-crystalline and two-dimensional perovskite barocaloric materials. The excellent BCE of the SCO compound {Fe(pz)2(BH3CN)2} is mainly due to its small molar mass, which makes the unit mass compound exhibit higher ΔSSCO, while the introduction of the third source of entropy change—the reorientation entropy change (ΔSreo), only plays a small role. This is expected to promote the practical application of SCO compounds as barocaloric refrigerants. [ABSTRACT FROM AUTHOR]

The idea of exploiting the inexhaustible solar energy-driven photocatalytic hydrogen evolution reaction (HER) to generate hydrogen energy, a sustainable clean energy source, to solve problems such as fossil fuel-induced greenhouse gas emissions is believed to be a feasible strategy. However, photocatalytic HER is inefficient due to insufficient light trapping capability and low charge separation efficiency of the single semiconductor material employed. Therefore, it remains a great challenge to achieve fast and efficient photocatalytic HER. In this work, a novel ternary Chl@Cu2O/Ti3C2Tx photocatalyst with an organic–inorganic heterojunction structure has been designed by employing a stepwise deposition process for efficient solar energy conversion to hydrogen. The results showed that the photocatalytic activity of Chl@Cu2O/Ti3C2Tx organic–inorganic heterojunction photocatalysts for HER was significantly improved compared with that of single Chl@Ti3C2Tx and Cu2O/Ti3C2Tx. The improvement of the photocatalytic performance of Chl@Cu2O/Ti3C2Tx compared to Chl@Ti3C2Tx and Cu2O/Ti3C2Tx is attributed to the construction of the Chl–Cu2O organic–inorganic heterojunction structure in Chl@Cu2O/Ti3C2Tx, which extends the absorption range of the spectra and dramatically enhances the separation efficiency of the photogenerated carriers in Chl@Cu2O/Ti3C2Tx composites. [ABSTRACT FROM AUTHOR]

[Display omitted] Ti 3 C 2 T x MXene, a new family of 2D materials, has been successfully used as an ideal co-catalyst for enhancing photocatalytic activity due to its excellent physicochemical properties. Bacteriochlorophyll (BChl), one of the most abundant photosynthetically active pigments, has been studied in the field of artificial photosynthesis due to its constant and efficient absorption of solar energy and conversion of the excitation energy into chemical energy. In this work, five BChl- a derivatives with a range of different side chain groups in the C17 substituent were prepared and deposited on the Ti 3 C 2 T x MXene surface by a solvent evaporation process to form BChl-n@Ti 3 C 2 T x (n = 1∼5) composite photocatalysts, which were used for the visible light-driven photocatalytic hydrogen evolution reaction (HER) in an aqueous solution. Among the five BChls investigated, BChl-5 possessing a quaternary ammonium terminal showed the best performance and BChl-5@Ti 3 C 2 T x composite exhibited an excellent hydrogen production activity of as high as 51 μmol/h/g cat. This is primarily attributed to the excellent photophysical and photochemical properties provided by the self-aggregation of BChl-5 in the BChl-5@Ti 3 C 2 T x composite and the outstanding charge transport capability of the 2D Ti 3 C 2 T x MXene. At the same time, the fast carrier separation and transfer capability between BChl-5 and Ti 3 C 2 T x provides reliable charge transport for photocatalytic HER. [ABSTRACT FROM AUTHOR]