NOVELTY - A catalyst (c1) comprises several porous clusters (c2) of silver particles, each cluster of the clusters including several primary particles (a1) of silver, and crystalline particles (b1) of zirconium oxide, where at least a portion of the crystalline particles of zirconium oxide is located in pores formed by a surface of the primary particles.    USE - In an air electrode useful as cathode in an electrochemical cell such as alkaline fuel cells, metal hydride anode alkaline fuel cells, metal-air rechargeable batteries, metal-air non-rechargeable batteries, oxygen sensors, and electrolysis cells (such as chlor-alkali cells (e.g. air/oxygen depolarized chlor-alkali cell)) (claimed); useful in air cathodes of electrochemical cells which are useful as power sources for back-up power, portable and emergency uses, electric vehicles, biomedical devices like hearing aids and cochlear implants, portable telecommunication devices for military and civilian use, portable electronic devices, pilot-less drones, and in the space program.    ADVANTAGE - The B.E.T. specific surface area of the silver-based catalyst is 3-16 (preferably 6-10) square meters per gram; an average agglomerate B.E.T. porosity of the catalyst is 30-50 (preferably 35-45)%; and a tap density of the catalyst is 1-3 (preferably 1.5-2.5) g/cc. The electrodes made with the silver catalyst and silver catalyst mix have advantages over prior art silver-catalyzed electrodes including longer life time, more robust structure and much higher stability porous structure permitting maintenance of the surface area under both the open circuit voltage (OCV) and closed circuit conditions, and also much improved capability to operate in the bi-functional mode in alkaline electrolytes. The air cathode may allow electrochemical cells, such as batteries and fuel cells, to last longer and significantly cuts their costs. The silver catalyst allows the production of carbon-less air cathodes thus making the cathode much more robust for extended life, easier manufacturing, and better durability. The catalyst also provides much higher power than non-precious metal catalysts like those based on manganese, cobalt, and nickel, at much lower cost than platinum. The carbon-less silver based catalyst electrode can be used as a direct drop-in replacement for conventional air cathodes in alkaline fuel cells and metal-air batteries to reduce cost and improve performance. One of the factors limiting the commercialization of rechargeable metal-air batteries is the presence of carbon in the cathode, which tends to oxidize and degrade during charging. Thus, the carbon-less cathode also enables development of rechargeable metal-air cells that are not otherwise viable.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an active catalyst mix (m1) including the catalyst (c1) and a water-repellent polymer;    (2) an air electrode (E1) comprising the active mix (m1) of silver catalyst (c1); a porous hydrophobic film and optionally an electrically conductive current collector having a specific electrical resistivity below 1x 10-5 ohm meters, where the active mix (m1) and the current collector are located together on a single broad face of the porous hydrophobic film, and bonded to the hydrophobic film;    (3) an electrochemical cell comprising an anode, the air electrode (E1) adapted to function as a cathode, and an electrolyte; and    (4) producing (M1) the nano-size silver catalyst (c1) promoted by zirconium oxide, involving providing a silver powder containing a porous agglomeration of silver particles having an average primary particle size of 150 nm; impregnating the agglomeration of silver particles by contacting the particles with an aqueous solution containing a zirconium (IV) compound selected from zirconium (IV) dinitrate oxide hydrate and zirconium (IV) dichloride oxide hydrate, so as to form a suspension; contacting the suspension with an aqueous alkaline solution (S1) to produce zirconium hydroxide, which precipitates in pores of the porous agglomeration; rinsing and drying the agglomerates with the zirconium hydroxide precipitated in the pores to produce a dried residual material, and heating the dried residual material at 250-300degrees C for 30-60 minutes to effect dehydration, and subsequently, heating at 400-550degrees C for 10-30 minutes to produce crystals of zirconium oxide, for forming the nano-size silver catalyst (c1) promoted by zirconium oxide.