Catalytically active metal and metal-alloy nanoparticles, such as Pt and Pt_xNi_y, play an important role inside the catalyst layers of various energy conversion devices, for instance polymer electrolyte membrane fuel cells (PEMFCs) and PEM electrolyzers. The catalytic activity and stability depend on various factors, such as the material properties, particle size and shape, and also the catalyst support. Various routes have been developed to fabricate such electrocatalyst nanoparticles mainly based on thermal, chemical and electrochemical approaches. In the thermal approach, catalyst precursor salts are thermally decomposed at several hundred degrees Celsius in a furnace, often under inert or reducing atmosphere. One promising alternative is the use of photonic curing (also known as flash light irradiation) where a Xe flash lamp provides under ambient conditions high energy light pulses with an emission spectrum ranging from around 300 nm up to 1000 nm. Depending on the light absorbing properties of the irradiated material, a thin film can be heated up to several hundred degrees Celsius on the millisecond scale [1]. This technique is usually applied to sinter metal nanoparticle deposits for flexible electronics.

Metal and metal alloy nanoparticles can be made by the photonic curing of the corresponding precursor salts in an indirect as well as direct way [2-4]. On the direct route, the absorption of the flash lamp light is only realized by a light absorbing support material while the coated precursor is not directly affected. The thermal decomposition of the precursor is then initiated by the heat transfer from the support material to the precursor. On the second route, the metal precursors absorb the light directly.

We made a detailed analysis of the photonic curing process for the direct formation of Pt and Pt alloy nano- and microparticles in terms of light absorbing properties of the precursor and support material, and we analyzed the influence of the precursor film thickness, wetness and spreading. Various light absorbing (e.g., carbon nanotubes) and non-absorbing (quartz glass) substrate materials have successfully been tested. In order to deposit well defined metal and metal alloy precursor layers, a state-of-the art inkjet printer platform with three parallel printheads and integrated photonic curing has been used. Dispensing metal precursor inks by using inkjet printing has already demonstrated its huge potential for printing of electrocatalyst materials [5]. We obtained combinatorial libraries of Pt and Pt alloy nano- and microparticles on a large scale within few minutes. The catalyst particles where then characterized using spectroscopic and electrochemical methods. Soft probe scanning electrochemical microscopy (SECM) [6] with arrays of contact mode microelectrodes was used for the rapid screening of the catalyst libraries in constant distance mode.

[1] K.A. Schroder, S.C. McCool, W.F. Furlan, NSTI Nanotech 2006 Technical Proceedings 2006, 3, 198 - 201.

[2] S. H. Park, H. S. Kim, J. Electrochem. Soc. 2015, 162, F204-F210.

[3] K. Jang, S. Yu, S. H. Park, H. S. Kim, H. Ahn, J. Alloys Compd. 2014, 618, 227-232.

[4] A. Lesch, V. Costa Bassetto, H. H. Girault, in preparation.

[5] E. Reddington, A. Sapienza, B. Gurau, R. Viswanathan, S. Sarangapani, E. S. Smotkin, T. E. Mallouk, Science 1998, 280, 1735-1737.

[6] A. Lesch, B. Vaske, F. Meiners, D. Momotenko, F. Cortés-Salazar, H. H. Girault, G. Wittstock; Angew. Chem. Int. Ed. 2012, 51, 10413-10416.