Multi-scale microscopy study of 3D morphology and structure of MoNi/MoO@Ni electrocatalytic systems for fast water dissociation.

The 3D morphology of hierarchically structured electrocatalytic systems is determined based on multi-scale X-ray computed tomography (XCT), and the crystalline structure of electrocatalyst nanoparticles is characterized using transmission electron microscopy (TEM), supported by X-ray diffraction (XRD) and spatially resolved near-edge X-ray absorption fine structure (NEXAFS) studies. The high electrocatalytic efficiency for hydrogen evolution reaction (HER) of a novel transition-metal-based material system - MoNi electrocatalysts anchored on MoO cuboids aligned on Ni foam (MoNi/MoO@Ni) - is based on advantageous crystalline structures and chemical bonding. High-resolution TEM images and selected-area electron diffraction patterns are used to determine the crystalline structures of MoO and MoNi. Multi-scale XCT provides 3D information of the hierarchical morphology of the MoNi/MoO@Ni material system nondestructively: Micro-XCT images clearly resolve the Ni foam and the attached needle-like MoO micro cuboids. Laboratory nano-XCT shows that the MoO micro cuboids with a rectangular cross-section of 0.5 × 1 µm and a length of 10-20 µm are vertically arranged on the Ni foam. MoNi nanoparticles with a size of 20-100 nm, positioned on single MoO cuboids, were imaged using synchrotron radiation nano-XCT. The application of a deep convolutional neural network (CNN) significantly improves the reconstruction quality of the acquired data.