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In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e −) from the cathode being given to hydrogen cations to form hydrogen gas. At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit.
Cathode reaction: O 2 + 4e − → 2O 2− Overall cell reaction: 2H 2 + O 2 → 2H 2 O. SOFC systems can run on fuels other than pure hydrogen gas. However, since hydrogen is necessary for the reactions listed above, the fuel selected must contain hydrogen atoms. For the fuel cell to operate, the fuel must be converted into pure hydrogen gas.
Faradaic losses describe the efficiency losses that are correlated to the current, that is supplied without leading to hydrogen at the cathodic gas outlet. The produced hydrogen and oxygen can permeate across the membrane, referred to as crossover. [13] Mixtures of both gases at the electrodes result. At the cathode, oxygen can be catalytically ...
The reaction at the cathode results in hydrogen gas and hydroxide ions: 2 H 2 O + 2 e − → H 2 + 2 OH −. Without a partition between the electrodes, the OH − ions produced at the cathode are free to diffuse throughout the electrolyte to the anode.
The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. [5] [6] Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode. Splitting of the hydrogen molecule is relatively easy by using a platinum ...
The hydrogen gas then diffuses back up through the cathode and is collected at its surface as hydrogen fuel, while the oxygen ions are conducted through the dense electrolyte. The electrolyte must be dense enough that the steam and hydrogen gas cannot diffuse through and lead to the recombination of the H 2 and O 2−. At the electrolyte-anode ...
When driven by an external source of voltage, hydrogen (H +) ions flow to the cathode to combine with electrons to produce hydrogen gas in a reduction reaction. Likewise, hydroxide (OH −) ions flow to the anode to release electrons and a hydrogen (H +) ion to produce oxygen gas in an oxidation reaction.
A proton-exchange membrane, or polymer-electrolyte membrane (PEM), is a semipermeable membrane generally made from ionomers and designed to conduct protons while acting as an electronic insulator and reactant barrier, e.g. to oxygen and hydrogen gas. [ 1 ] This is their essential function when incorporated into a membrane electrode assembly ...