TiO₂ coated complex 3D Foams: Physical properties and photocurrent generation mechanisms

The synthesis of functional material (e.g. TiO₂) on foams is a becoming an important research area, particularly in photocatalysis. However, photocatalytic coatings on foams are most of the time synthesised using the sol-gel and soft template methods. PVD-based methods are rarely used to deposit photocatalytic coatings on such substrates and when they are, the growth mechanisms are never mentioned. However, PVD deposition can bring significant breakthroughs when using such 3D substrates, like accurate control and tuning of film morphology, composition, and/or synthesis of metastable phases. This work is a comprehensive study of the film growth on complex 3D substrates. TiO₂ films have been deposited on Ni and C foams by magnetron sputtering in different discharge modes (DC transition regime, DC fully reactive, and HiPIMS) to understand the correlation between discharge parameters, covering of the foam, and photocatalytic performance of coated substrate. Depending on the choice of deposition parameters, the structure is tuned between anatase, or a mix of rutile and anatase, with the possibility to synthesise highly unstable {001} crystal facets. SEM cross-sections of the TiO₂@C foam assemblies allow to observe the change in coating morphology with increasing depth inside the foam. The photoelectrochemical measurements, combined with the XRD results, highlight the superior photocurrent generation provided by the coatings deposited using DC magnetron sputtering in the transition regime, as they display a well-crystallised anatase structure with a large amount of highly photocatalytically active {001} facets.