Electrodeposition of Catalyst Nanowires on Microporous Substrate for PEMFC

SIBIUDE, F. GALDRIC; GUILLET, NICOLAS; NORES PONDAL, FEDERICO J.; BIDAN, GÉRARD; AL-HOSHAN, MANSOUR

Montreal

Conferencia; 219th ECS Meeting; 2011

Electrochemical Society

Electrodeposition of catalyst nanowires on microporous substrate for PEMFC Galdric SIBIUDE1, Nicolas GUILLET1,  Federico NORES PONDAL1, Gérard BIDAN2,  Mansour ALHOSHAN3Commissariat à l’Energie Atomique et aux Energies Alternatives 1CEA-Grenoble/LITEN  2CEA-Grenoble/INAC 17, rue des Martyrs, 38054 Grenoble Cedex 9, FRANCE 3 King Saud University, College of Engineering  PO Box 800,Riyadh 11421, Kingdom of Saudi Arabia galdric.sibiude@cea.fr  Decreasing  the  platinum  loading  is  one  of  the required conditions to make PEMFC economically viable. Nanostructuration  of  particle  greatly  enhances  the  mass catalytic  activity  by  increasing  the  surface  area.  For  this reason,  nanostructuration  presents  a  growing  interest  to improve the yield in fuel cells and decrease the amount of precious metals.  Platinum   nanowires   directly   grown   on   gas diffusion layer are of prime interest since the deposit can simply be used as an electrode, allowing gases and water flows,    without    any    post-treatment.    A    templated electrodeposition way of making this kind of structure is proposed   and   the  first  physical   growth   phenomenon understandings will be discussed. The process offers new and   practical   possibilities   in   fuel   cell   application compared with the classical template electrodeposition on thin  films[1].  It  leads  to  nanowire-brush  structure  with single diameter from 100nm to 30nm (Figure 1).  Figure 1: SEM side view of electrodeposited platinum nanowires on microporous substrate through an 80nm-diameter pores matrix The advantage of the process is the possibility to control the pattern of the deposit by controlling the matrix porosity and the electrodeposition parameters. That would potentially  lead  to  a  better  distribution  of  the  catalyst  in the  active  layers  by  locating  it  at  the  best  places  and enhance gases and water diffusion[5]. Nanowires  are  expected  to  show  high  catalytic performance [2] as well as durability. At the moment, the use  of  such  a  structure  gives  promising  performances towards oxygen reduction reaction (Figure 2) (j (0,9V)  = 150 µA.cm Pt-2  at  25°C  similar  to  Pt  nanoparticles[3])  at  low platinum  loading  (j (0,9V)   =  26  mA.mg Pt-1).  This  easy process[4] allows us to quickly transfer the deposit in half-cell  or  fuel  cell  test  by  hot  pressing  on  a  polymer electrolyte membrane.  Cyclic voltammetry-60-50-40-30-20-100700 800 900 1000 1100E/mV vs RHEj/mA.cm-2under nitrogenunder oxygenFigure 2: Cyclic voltammetry under nitrogen and oxygen in half-cell conditions (25°C, 101kPa, electrolyte H 2 SO 4  0.5M) Studies  have  been  performed  to  investigate  the influence  of  the  different  electrodeposition  parameters. Particularly, the reaction yield versus deposition potential has  been  analysed  for  a  constant  charge.  Finally,  it  has been  shown  that  fixing  the  applied  potential  and  the amount  of  charge  used  for  electrodeposition  of  platinum allows  us  to  get  a  better  control  of  the  amount  of deposited platinum.  A prime problem to solve is the presence of free volumes at the matrix/microporous interface that have to be filled in. To do so, we are exploring the use of support materials for platinum catalysts that could be used to fill in  those  free  volumes  (non  noble  metals,  conducting polymers).  This  is  the  strategy  currently  followed  to improve  the  catalyst  deposit  architecture  and  the  first preliminary  tests  in  fuel  cell  to  evaluate  its  performance are being performed. The  understanding  of  growth  mechanism  could lead   to   a   better   comprehension   and   control   of   the architecture. For example, the evidence of the end of free volume filling on current curve could allow the deposition of  a  precise  quantity  of  a  third  material.  Finally,  the difficulty  of  non-flat  substrate  deposition  as  well  as  its great  advantage  in  different  applications  (particularly  in energy conversion and storage) will be highlighted.  Experiments are also being carried out to explore other innovative catalyst nanowires (bimetallics, platinum monolayer  on  a  metal  nanowire...).  The  use  of  such structures  is  motivated  by  going  further  in  platinum loading  reduction.  First  results  will  be  presented  (see Figure 4).  Figure 4: SEM images of successive electrodeposited palladium and platinum nanowires on microporous substrate through a 50nm-diameter pores matrixREFERENCES [1] S. M. Choi, et al. Electrochimica Acta 53 (19):5804-5811, 2008 [2] M. Subhramannia, et al. Journal of Materials Chemistry 18:5858-5870, 2008 [3] H.A. Gasteiger, et al. Applied Catalysis B: Environmental 56: 9–35, 2005 [4] French patent PCT/FR2009/001341 [5] A.A. Franco, et al. Journal. of the Electrochemical Society 156(3): B410-B424, 2009 2µm  300nm 1µm  100nm