Nano-structured Electrodes Improve Mechanical Strength and Reduce Cost for Solid Oxide Fuel Cells

Institute of Nuclear Energy Research Atomic Energy Council, Executive Yuan (Taoyuan County, TW) researchers have developed a solid oxide fuel cell comprising a nano-structured electrode with a metal support operating at intermediate temperature and a manufacturing method. The solid oxide fuel cell has excellent electric characteristics and high thermal conductivity by using a metal support, say inventors Chang-Sing Hwang and Chun-Huang Tsai in U.S. Patent Application 20100098996. The metal frame and the porous metal substrate are combined to improve the mechanical strength and flatness of the cell for formation of a cell stack.

Hwang and Tsai developed a manufacturing method for the solid oxide fuel cell using a tri-gas atmospheric plasma spray with a medium current and high voltage spray gun to improve thin film quality and efficiency. The plasma flame by the medium current and high voltage tri-gas atmospheric plasma spray process exhibits a longer plasma arc to lengthen the time for heating the powder clusters by the high-temperature plasma flame so that the powders are heated up more efficiently to be deposited to form a thin film with better quality. More particularly, the thin film as formed exhibits more tri-phase boundaries (TPB) and stronger mechanical strength. Moreover, the tri-gas atmospheric plasma spray process is performed in a medium current and high voltage environment. Since the working current is smaller, the electrode erosion of atmospheric plasma spray gun is reduced and the lifetime of the atmospheric plasma spray gun can be lengthened to reduce cost.

The solid oxide fuel cell includes a metal frame, a pre-treated porous metal substrate, an anode layer, an electrolyte layer, a cathode interlayer and a cathode current collecting layer. The pre-treated porous metal substrate is disposed inside the metal frame. The anode layer is disposed on the porous metal substrate. The electrolyte layer is disposed on the anode layer. The cathode interlayer is disposed on the electrolyte layer. The cathode current collecting layer is disposed on the cathode interlayer. The anode layer is porous and nano-structured.  

The solid oxide fuel cell anode is made of electron-conducting nano-particles and is comprised of nano nickel, nano copper, nano nickel-copper or nano nickel-copper-cobalt, and the anode ion-conducting nano-particles comprise nano yttria-stabilized zirconia (YSZ), nano lanthanum doped ceria (LDC) or nano gadolinium doped ceria (GDC).

The nano-structured anode layer and the nano-structured cathode interlayer provide a plurality of nano tri-phase boundaries (TPB) to improve the cell electric characteristics while lowering the working temperature of a solid oxide fuel cell.

The supporting structure of the solid oxide fuel cell is composed of a porous metal substrate and a metal frame so as to increase resistance to cell deformation at high temperatures, cell flatness, cell mechanical strength, supporting strength for cell stack manufacture and thermal conductivity of cell and stack. Moreover, the anode layer and the cathode interlayer of the solid oxide fuel cell are formed of a composite nano-structure comprising nano-particles. Therefore, The electrochemical reaction activities and conductivities of anode and cathode electrodes can be improved with lowered electrode resistances to reduce power consumption. Moreover, the lifetime of the electrode structure is lengthened because the aggregation of each component at high temperatures in the well mixed and nano-structured electrode is prohibited by other component.

Nano-structured micron powder clusters formed by aggregating nano powders with diameter smaller than 100 nm with a polyvinyl alcohol (PVA) binder are injected into the plasma flame of the medium current and high voltage tri-gas atmospheric plasma spray (APS). The plasma flame removes the polyvinyl alcohol (PVA) binder and heats up the remained nano powders. In the plasma flame, since nano powders exhibit a larger surface area, it helps the nano powders to be heated up uniformly to be melted or semi-melted. The manufactured nano-structured layer does not only provide better functionality due to the nano structure, but also reduce the amount of powders for atmospheric plasma spray and thus the cost for manufacturing the solid oxide fuel cell can be also reduced.