Improved adsorption cooling performance of MIL-101(Cr)/GO composites by tuning the water adsorption rate

Abstract

An adsorption cooling system (ACS) driven by low-grade waste thermal and solar energy has the advantages of low carbon emission and reduced electricity consumption. Metal–organic frameworks (MOFs) with ultrahigh surface areas are recognized as the most potential adsorbents for an adsorption cooling system (ACS) owing to their excellent water adsorption capacity. Nevertheless, a vast majority of previous studies focused on increasing the water uptake of MOFs in order to improve adsorption cooling performance. In practice, fast water adsorption plays a more important role in determining cooling performance than water uptake. In this work, water-stable MIL-101(Cr) was integrated with different contents of graphene oxide (GO) to obtain large-pore MIL-101(Cr)/GO composites for an improved water adsorption rate, leading to enhanced cooling performance. It is found that the trade-off between increased pore size and reduced hydrophilicity upon GO incorporation leads to the improved water adsorption rate of MIL-101(Cr)/GO composites. Moreover, both specific cooling power (SCP) and the coefficient of performance for cooling (COP_C) of MIL-101(Cr)/GO composites were improved compared with those for pristine MIL-101(Cr). SCP of MIL-101(Cr)/GO composites is dominated by the water adsorption rate, and the MIL-101(Cr)/GO-10 composite containing 10 wt% GO exhibited the highest SCP, which is approximately 1.5 times that of MIL-101(Cr). COP_C exhibited a dissimilar trend with the water adsorption rate and SCP since it is affected by both the water adsorption rate and thermophysical properties including heat of adsorption and heat capacity of adsorbents.