Towards the Industrial Application of Spark Ablation for Nanostructured Functional Materials

Abstract

Nanostructuring of functional materials is an essential part in the design of energy related devices – but the industrial tools we have to make these materials are lacking. This dissertation explores the green, flexible, and scalable spark discharge process for the fabrication of complex nanostructured materials, and the application of said materials in energy devices. A novel spark generator concept with a 60-fold increased mass production rate was developed, where spark energy and spark repetition rate have been decoupled from gas and material properties. The application of spark discharge materials in two types of energy storage and conversion devices was studied: amorphous-Si photovoltaic cells, MgH2-based hydrogen storage. The possibility of using spark discharge to functionalize nanoparticles with metal coatings was investigated using two spark generators in series. The new spark generator provides true scaling: it produces materials identical to that of the old designs, and the mass production rate – about a gram per day – scales linearly with the spark repetition rate. Arrays of ?100 nm high-purity silver nanospheres were deposited as scattering agents in solar cells, improving their external quantum efficiency by 30 %. A method for synthesizing MgH2 nanoparticles was developed, which show promising hydrogen storage properties. Nanocomposites of Mg with NbOx catalyst nanoparticles were synthesized using two sparks in series, increasing the H2 desorption rate of MgH2. Using a hollow electrode spark, 40 nm gold nanoparticles were coated with silver, and vice versa. The possibility to make useful quantities of high-quality nanomaterials – e.g. high-purity metals or light metal hydrides – from nearly any element makes spark discharge a powerful tool in materials design. The new spark generator provides sufficient quantities to make it economical to develop an industrial nanoparticle facility using multiple sparks in parallel.