Preheat oven to 325 degrees. Grease and flour a bundt pan.
In a large measuring cup or bowl, dissolve the baking soda in the water. Add the coffee and vanilla. Stir.
Whisk the cocoa, cinnamon, and cayenne pepper.
In a mixer or large bowl, cream together the butter and sugar until very light and fluffy. Beat in the cocoa and spice mixture. Add egg yolks one at a time.
Alternately add the flour and coffee mixture until just combined, ending with flour.
Beat egg whites until stiff peaks form. Make sure they are stiff!
Add egg whites to batter 1/2 at a time until no white streaks remain.
Pour batter into prepared bundt pan and bake for 1 hour or until a toothpick inserted into the center of the cake comes out clean.
Let cake cool in pan set on a wire rack at least 20 minutes. Turn out onto a cake plate and dust with powdered sugar.