The MXene/water nanofluids with high stability and photo-thermal conversion for direct absorption solar collectors: A comparative study

The efficient utilization of solar energy is a prominent problem in the field of energy in today’s society. The judicious combination of nanofluid and direct absorption solar collector (DASC) is one of the effective ways to solve this problem. Two-dimensional nanomaterials have attracted significant research attentions because of their unique optical and thermophysical properties. In this paper, two-dimensional MXene nanosheets were prepared by in-situ etching. Then different concentrations (5, 10, 20, 40, 60 ppm, respectively) of MXene and graphene nanofluids were obtained by two-step method. The optical and thermal conductivity of the two nanofluids were further tested. The MXene nanofluids exhibited advanced optical properties due to the LSPR effect of MXene nanosheets, but the graphene nanofluids had higher thermal conductivity. When the concentration was 20 ppm, the photothermal conversion efficiency of MXene nanofluids reached a maximum of 63.35%, which was 4.34% higher than that of graphene nanofluids. Finally, through the analysis of local conversion efficiency, the working conditions of DASC were further optimized. •Nanofluids containing multilayer MXene nanosheets were prepared.•MXene nanofluids exhibit better stability than graphene nanofluids.•Optical properties of MXene nanofluids were discussed systematically.•The photo-thermal conversion efficiency of MXene nanofluids was 63.35% at 20 ppm.