Fuel cells utilizing liquid sodium-potassium alloy (NaK) reducing agent and fuel cell systems including the same. The fuel cells include a housing defining a housing volume and a reducing agent-containment structure defining a reducing agent-containment volume. The fuel cells also include a volume of NaK reducing agent extending within the reducing agent-containment volume and an anode conductor extending in electrical contact with the NaK reducing agent such that the NaK reducing agent forms at least a portion of an anode electrode of the fuel cell. The fuel cells further include a cathode electrode that extends within the housing volume and is spaced-apart from the NaK reducing agent, an electrolyte present within the housing volume, and an oxidizing agent supply structure configured to provide an oxidizing agent to the housing volume.