Long-Term Solar Energy Storage under Ambient Conditions in a MOF-Based Solid–Solid Phase-Change Material

Abstract

This paper demonstrates a metal–organic framework (MOF) containing photoswitches within the pores as a hybrid solar thermal fuel (STF) and solid–solid phase-change material (ss-PCM). A series of azobenzene-loaded MOFs were synthesized with the general formula Zn2(BDC)2(DABCO)­(AB) x (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]­octane, AB = azobenzene, where x = 1.0, 0.9, 0.5, 0.3), herein named 1⊃AB1.0, 1⊃AB0.9, 1⊃AB0.5, and 1⊃AB0.3 respectively. X-ray powder diffraction, solid-state NMR, and density functional theory calculations were used to explore in detail the structural changes of the host framework that take place upon loading with the AB guest molecules. Differential scanning calorimetry measurements reveal a reversible phase change, which is absent from the evacuated framework. Upon irradiation with 365 nm light, 40% of the AB guests converted from the trans to the higher-energy cis isomeric form in 1⊃AB1.0. The energy stored within the metastable cis isomers is released upon heating and balances the endotherm associated with the phase transition. However, the exotherm associated with the phase transition is retained upon cooling, resulting in a net energy release over a full heating–cooling cycle. The maximum energy density is observed for the fully loaded composite 1⊃AB1.0, which releases 28.9 J g–1. In addition, the cis-AB guests in this composite showed negligible thermal reconversion during 4 months at ambient temperature, with an estimated energy storage half-life of 4.5 years. Further development of MOF-based STF-ss-PCMs could lead to applications for solar energy conversion and storage, and thermal management.

Efficient solid-state photoswitching of methoxyazobenzene in a metal–organic framework for thermal energy storage

“…In the 13 C cross-polarisation (CP) magic-angle spinning (MAS) NMR spectrum of 1IMOAB (Fig. 2a and S14-S16 †), single DABCO and carbonyl resonances at 47.6 and 171.2 ppm are consistent with those previously observed for the np orthorhombic structure of 1IAB.…”

“…MOAB was occluded within the pores of 1 by a previously described melt-inltration procedure. 13,37 The maximum loading level obtained was 1.25 MOAB molecules per pore (Fig. S1, S2 and Tables S1-S3 †).…”

“…10 Recently, connement within metal-organic frameworks (MOFs) has been shown as an effective way to impart conformational freedom to photoswitches within bulk solid materials. Using this approach, solid-state photoswitching has been demonstrated for AB derivatives [13][14][15][16][17][18][19][20][21][22] as well as other molecules including dithienylethenes, [23][24][25][26][27] 2-phenylazopyridine, 28 and spiropyrans. [29][30][31][32][33][34][35] In addition to spatial considerations, another requirement for solid-state MOST materials is to ensure a high degree of photoconversion to the metastable state.…”

Optically controlled large-coercivity room-temperature thin-film magnets

“…The azobenzene moiety has been investigated in the context of metal-organic framework (MOF) materials either as an intrinsic linker or a kind of surface additive. [34][35][36] Most related to the present study, we recently demonstrated a photo-switched water molecule capture/release behavior for ALD/MLD-grown MOF-like Feazobenzene thin films. 34 In the present work we now embed separate azobenzene layers in the ferrimagnetic ε-Fe 2 O 3 matrix for well-defined superlattice (SL) structures to challenge the photocontrol of the unique magnetic properties of the ε-Fe 2 O 3 phase.…”

Modelo de optimización LFSR basado en método de coeficientes adaptativos para sistemas reconfigurables de ERNC

“…Fotovoltaica: Recientes investigaciones [29] presentan la aplicación de un material cristalino, basado en un tipo de marco orgánico-metálico -MOF, una red de iones metálicos unidos por moléculas basadas en el carbono para formar estructuras tridimensionales, estos pueden formar materiales compuestos, al contener otras pequeñas moléculas, dentro de sus estructuras, que le permiten capturar energía, los investigadores expusieron el material a la luz UV, encontrando que la energía potencial puede almacenarse durante largos períodos de tiempo a temperatura ambiente y se puede liberar a demanda.…”