1e:T496,Scalable and sustainable solar hydrogen production through photocatalytic water splitting requires highly active and stable earth-abundant co-catalysts to replace expensive and rare platinum. Here we employ density functional theory calculations to direct atomic-level exploration, design and fabrication of a MXene material, Ti₃C₂ nanoparticles, as a highly efficient co-catalyst. Ti₃C₂ nanoparticles are rationally integrated with cadmium sulfide via a hydrothermal strategy to induce a super high visible-light photocatalytic hydrogen production activity of 14,342 μmol h^-1g^-1 and an apparent quantum efficiency of 40.1% at 420 nm. This high performance arises from the favourable Fermi level position, electrical conductivity and hydrogen evolution capacity of Ti₃C₂ nanoparticles. Furthermore, Ti₃C₂ nanoparticles also serve as an efficient co-catalyst on ZnS or Zn_xCd_1-xS. This work demonstrates the potential of earth-abundant MXene family materials to construct numerous high performance and low-cost photocatalysts/photoelectrodes.1f:T457,Achieving high sensitivity in solid-state gas sensors can allow the precise detection of chemical agents. In particular, detection of volatile organic compounds (VOCs) at the parts per billion (ppb) level is critical for the early diagnosis of diseases. To obtain high sensitivity, two requirements need to be simultaneously satisfied: (i) low electrical noise and (ii) strong signal, which existing sensor materials cannot meet. Here, we demonstrate that 2D metal carbide MXenes, which possess high metallic conductivity for low noise and a fully functionalized surface for a strong signal, greatly outperform the sensitivity of conventional semiconductor channel materials. Ti₃C₂T_x MXene gas sensors exhibited a very low limit of detection of 50-100 ppb for VOC gases at room temperature. Also, the extremely low noise led to a signal-to-noise ratio 2 orders of magnitude higher than that of other 2D materials, surpassing the best sensors known. Our results provide insight in utilizing highly functionalized metallic sensing channels for developing highly sensitive sensors.

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