Higher-order nanostructures of two-dimensional palladium nanosheets for fast hydrogen sensing

Two-dimensional (2D) materials often show a range of intriguing electronic, catalytic, and optical properties that differ greatly from conventional nanoparticles. While planar configuration is often desirable, a range of applications such as catalysis and sensing benefit greatly from the accessibility to large surface areas. The 2D materials generally tend to form stacks in order to reduce the overall surface energy. Such densely packed structures however are detrimental when access to high surface area is required. Herewith we demonstrate a chemical strategy to generate Pd three-dimensional (3D) structures from its flexible 2D nanosheets. Solvent polarity is shown to play an important role to control the final morphology of these nanosheets. Our data indicate when these Pd 3D materials were integrated into hydrogen sensing devices, response time was found to be an order of magnitude faster than their 2D-constrained counterparts. The easy accessibility to the surfaces by hydrogen gas is considered to be an important factor for the observed fast response time based on the sensing model.