Developed novel catalysts has been enhanced its activity and durability by researchers. There are some approaches to enhance Pt activity such as alloy, core-shell, and nanoframe and to improve durability by covered catalysts such as Silica, carbon, and organic compound. However, as for evaluation of catalyst, it is generally difficult to reflect half-cell results to membrane electrode assembly (MEA) one after screening of catalysts in electrolyte by half-cell method. There is morphology of catalyst layers (CLs) structure such as secondary porous, tortuosity, and porosity in addition to morphology of catalysts such as Pt specific surface, activity, and carbon support pore. Therefore, it is necessary to design CLs to bring out the performance without loss(1,2). The amount of ionomer around Pt/C is focused. It is also important factor influencing CLs structure. Although ionomers contribute the proton conduction, an excess of it prevents diffusion of oxygen to decrease porosity. Thus, decreasing ionomer amount is better in terms of oxygen diffusion. However, it is difficult to prepare the CLs loading low amount of ionomers by typical coating method since ionomers have a role in binding between secondary particles and increasing viscosity of ink. The catalyst by coverage Silica layer produced by Takenaka et al. is focused. Covering silica is one of the useful method to improve durability of Pt/C(3,4). The surface characteristics is transmuted by covering silica on the Pt/C. And then, it is available to keep the good dispersion ink even if low ionomer/carbon mass ratio (I/C). In this work, CLs with low I/C and effect of silica coating is evaluated by output performance using catalyst covered silica layer.

CLs was prepared using by inkjet method. I/C enable to be reduced down to 0.25 in standard sample (TEC10V50E, Tanaka kikinzoku kogyo). Below this value, it is difficult to prepare the CLs to agglomerate the secondary particles since ionomers is not enough as a binder. As for silica catalyst, it is available to reduce I/C down to 0.05 while ink keeps good dispersion. The dispersibility is enhanced by difference between surface characteristics. Low I/C samples were showed performance same as typical method of I/C = 1.0 in high humidity. It is possible to get the good performance with low I/C. In addition, output covered silica layer is better than standard sample in low humidity. The result indicates that silica plays a role in humectant-like.

1. Inoue and M. Kawase, J. Power Sources, 327(14), 1, (2016).
2. Kotoi, G. Inoue, and M. Kawase, ECS Trans., 75, 385, (2016).
3. Takenaka, H. Matsumori, K. Nakagawa, H. Matsune, E. Tanabe, and M. Kishida, J. Phys. Chem. C, 111(42), 15133, (2007).
4. Takenaka, H. Matsumori, T. Arike, H. Matsune, and M. Kishida, Top. Catal., 52(6-7), 731, (2009).