CNTs can also be combined with MXene nanosheets on a nanoscale level, making 2-D/1-D composites composed of alternating layers of individual MXene sheets/CNTs, for applications including battery electrodes and separators, 167 supercapacitors, 168 EMI shielding, 169 water splitting, 170 and sensors. In these materials, CNTs are used for a variety of reasons, including to control the spacing between MXene sheets and to prevent sheets from restacking (to improve ion transport in battery electrodes, for example), to improve mechanical properties such as tensile strength, 166, 174 electrical conductivity, 170 and electromagnetic shielding and absorption. CNTs can also be used as a strategy for embedding metallic nanoparticles between MXene sheets. Turning to the "Applications" branch, energy storage is the most active area in terms of total number of publications, with battery research driving much of that growth, as shown in Figure . Other notable application areas with a large number of publications in 2020-2022 include sensors, environmental, and biomedical (Supplementary Figure ). Fewer total publications, but more rapid growth, is seen in electronics and energy conversion applications. Full time trends of journal and patent documents in these areas are shown in Figure .