Supplementary Figure 1 illustrates the operation principle of a single chamber fuel cell (SCFC) using a propane-air mixture. The anode and cathode are in the same chamber and exposed to the same air-propane mixture. The anode is active and selective for propane partial oxidation and electro-oxidation of the resulting H₂ and CO. The reactions at the anode are: C₃H₈ + 3/2O₂ → 3CO + 4H₂, CO + O²⁻ → CO₂ + 2e⁻, and H₂ + O₂ → H₂O + 2e⁻. The cathode is active and selective for oxygen electro-reduction: 1/2O₂ + 2e⁻ → O²⁻. Although both electrodes are exposed to the same gases, their differing catalytic and electrocatalytic activities towards propane and oxygen create an oxygen partial pressure gradient across the fuel cell, generating a voltage for power generation. Due to the exothermic nature of the partial oxidation reaction, the fuel cell temperature can be up to 245°C higher than that of the furnace used to fix the fuel cell temperature. Ideal electrodes are active only for desired reactions and inert to others. The ideal cathode does not catalyze propane oxidation. [S6, 1]Supplementary Figure 1 illustrates the operation principle of a single chamber fuel cell (SCFC) using a propane-air mixture. The anode and cathode are in the same chamber and exposed to the same air-propane mixture. The anode is active and selective for propane partial oxidation and electro-oxidation of the resulting H₂ and CO. The reactions at the anode are: C₃H₈ + 3/2O₂ → 3CO + 4H₂, CO + O²⁻ → CO₂ + 2e⁻, and H₂ + O₂ → H₂O + 2e⁻. The cathode is active and selective for oxygen electro-reduction: 1/2O₂ + 2e⁻ → O²⁻. Although both electrodes are exposed to the same gases, their differing catalytic and electrocatalytic activities towards propane and oxygen create an oxygen partial pressure gradient across the fuel cell, generating a voltage for power generation. Due to the exothermic nature of the partial oxidation reaction, the fuel cell temperature can be up to 245°C higher than that of the furnace used to fix the fuel cell temperature. Ideal electrodes are active only for desired reactions and inert to others. The ideal cathode does not catalyze propane oxidation. [S6, 1]