Fuel cells are stacked to achieve the required voltage and power output levels. There are two main types of stacking: planar-bipolar stacking and stacking with tubular cells. In planar-bipolar stacking, individual fuel cells are connected with interconnects that serve as both electrical connections and gas barriers between adjacent cells. The gas flow in planar-bipolar stacks can be arranged in cross-flow, co-flow, counter-flow, serpentine flow or spiral flow configurations. Stacking with tubular cells is especially suitable for high-temperature fuel cells and has advantages for sealing and structural integrity, but presents geometric challenges for power density and current paths.

1. 1.3- Fuel Cell Stacking
Stacking to achieve the voltage and power output level required.
- Planar-Bipolar Stacking
- Stacks with Tubular Cells
1.3.1- Planar-Bipolar Stacking
Individual unit cells are electrically connected with interconnects.
Because of the configuration of a flat plate cell, the interconnect
becomes a separator plate with two functions:
- to provide an electrical series connection between adjacent
cells, specifically for flat plate cells.
- to provide a gas barrier that separates the fuel and oxidant
of adjacent cells.

2. 1.3- Fuel Cell Stacking
1.3.1- Planar-Bipolar Stacking
Figure 1-2 Expanded View of a Basic Fuel Cell Unit in a Fuel Cell Stack (1)

3. 1.3- Fuel Cell Stacking
1.3.1- Planar-Bipolar Stacking
Planar-bipolar stacks can be further characterized according to
arrangement of the gas flow:
• Cross-flow. Air and fuel flow perpendicular to each other
• Co-flow. Air and fuel flow parallel and in the same
direction. In the case of circular cells, this means the
gases flow radially outward
• Counter-flow. Air and fuel flow parallel but in opposite
directions.
• Serpentine flow. Air or fuel follow a zig-zag path
• Spiral flow. Applies to circular cells

4. 1.3- Fuel Cell Stacking
1.3.2 Stacks with Tubular Cells
- Especially for high-temperature fuel cells
- have significant advantages in sealing and in the structural
integrity of the cells.
- geometric challenge to the stack designer for high power
density and short current paths.
- The cell arrays can be connected in series or in parallel.
1.3.1- Planar-Bipolar Stacking
The manifold of gas streams to the cells in bipolar stacks can be
achieved in various ways:
- Internal: the manifolds run through the unit cells
- Integrated: the manifolds are integrated in the interconnects
- External: the manifold is completely external to the cell.