Development of photocatalytic and electrocatalytic coatings via thermal spraying for environmental and energy storage applications: a short review

With the development of society, human beings are facing environmental problems and an energy crisis worldwide. In this context, photocatalysis and electrocatalysis represent promising technologies to help solving these issues. Up to now, most of the catalysts intended for these usages are prepared via time-consuming wet-chemical approaches, e.g. hydrothermal or sol–gel methods. Moreover, these techniques produce powdery catalysts which need not only a post-filtration step, but also a shaping by a binder for their final applications, which makes the manufacturing cumbersome. Thermal spraying is currently a well-established deposition technique that is capable of elaborating a wide series of functional coatings based on all classes of materials (metals, polymers, ceramics) and featuring tunable compositions as well as micro- and nanostructures. In particular, thermal involving liquid feedstock, and more specifically precursor solutions or suspensions, have allowed generating a wide range of coating thicknesses, from the ten-micron to the submicron/nano scale, increasing thereby the possibilities for enhancing catalytic performances. The present review sets out marking researches relating to the preparation and testing of (i) some photocatalytic coatings intended for the degradation of aqueous organic pollutants and (ii) electrocatalytic coatings investigated as potential energy storage devices. This paper will not only deal with the preparation of catalysts via different thermal spray processes, but also will cover the adjustment of phase compositions and microstructures that are rendered possible when using liquid feedstock thermal spray techniques with the prospect of optimizing the catalytic performances.