In a metal air battery, metal works as the anode while oxygen works as the cathode. What is the role of the catalyst then and how does it work in a metal air battery?
The links provided above are definitely good starting points, but the idea of "facilitating" ORR and OER is complicated. It largely depends on the system that you are interested in and to some extent the electrolyte. In a typical cell the metal ion (ie. Li+, Na+) reacts with O2 at the oxygen electrode surface (here we call it an "oxygen electrode" since technically the "cathode" is O2) to produce a metal-oxide (superoxide, peroxide, hydroxide etc.). The metal-oxide that is produced exhibits varying levels of stability based on its environment, but is most commonly solid. That solid species is typically poorly conductive, so when it deposits on the electrode, it progressively covers active reaction sites. Introducing a catalyst to the oxygen electrode surface serves a few functions: 1) it reduces the overpotentials of ORR or OER so that the energy efficiency of the cell is better and 2) it may change the morphology or stoichiometry of the metal-oxide product (usually making it more reversible). There are additional effects that are influenced by catalyst selection such as reducing electrode pore blocking and stabilizing reaction intermediates, but those are related to the points above. If you are interested in catalysts for Li-O2 systems, please take a look at some of my recent papers. Hope this helps!
Article Catalyst and electrolyte synergy in Li-O2 batteries
Article Operando Observation of the Gold-Electrolyte Interface in Li...
The links provided above are definitely good starting points, but the idea of "facilitating" ORR and OER is complicated. It largely depends on the system that you are interested in and to some extent the electrolyte. In a typical cell the metal ion (ie. Li+, Na+) reacts with O2 at the oxygen electrode surface (here we call it an "oxygen electrode" since technically the "cathode" is O2) to produce a metal-oxide (superoxide, peroxide, hydroxide etc.). The metal-oxide that is produced exhibits varying levels of stability based on its environment, but is most commonly solid. That solid species is typically poorly conductive, so when it deposits on the electrode, it progressively covers active reaction sites. Introducing a catalyst to the oxygen electrode surface serves a few functions: 1) it reduces the overpotentials of ORR or OER so that the energy efficiency of the cell is better and 2) it may change the morphology or stoichiometry of the metal-oxide product (usually making it more reversible). There are additional effects that are influenced by catalyst selection such as reducing electrode pore blocking and stabilizing reaction intermediates, but those are related to the points above. If you are interested in catalysts for Li-O2 systems, please take a look at some of my recent papers. Hope this helps!
Article Catalyst and electrolyte synergy in Li-O2 batteries
Article Operando Observation of the Gold-Electrolyte Interface in Li...
catalysis in metal air battery is not fully understood, because true catalytic effect is seldom observed in metal air battery which should be related with decrease in over potentials of charge and discharge.
However a catalyst should facilitate in Electrochemical reduction or oxidation of oxygen by reducing either adsorption, electronic or mass transfer barriers
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