NOVELTY - The apparatus comprise a cell, and a power supply. The cell includes a sonication bath, and a chamber, and is configured to maintain an atmosphere of inert gas. The chamber is submerged in the sonication bath, and comprises upper and lower compartments separated by a microporous material. The upper compartment comprises a cover, a working electrode, a platinum foil contact, a reference electrode, and a counter electrode. The working electrode is electrically connected to the platinum foil contact. The platinum foil contact is electrically connected to the microporous material.    USE - The apparatus is useful: for depositing ultrathin films on nanoparticles, which are useful in energy conversion devices such as fuel cells, metal-air batteries and supercapacitors; and as a batch or a continuous reactor.    ADVANTAGE - The apparatus ensures effective, simple and economical deposition of the ultrathin films on the nanoparticles with less energy consumption.    DETAILED DESCRIPTION - The apparatus comprise a cell, and a power supply. The cell includes a sonication bath, and a chamber, and is configured to maintain an atmosphere of inert gas. The chamber is submerged in the sonication bath, and comprises upper and lower compartments separated by a microporous material. The upper compartment comprises a cover, a working electrode, a platinum foil contact, a reference electrode, and a counter electrode. The working electrode is electrically connected to the platinum foil contact. The platinum foil contact is electrically connected to the microporous material. The lower compartment comprises an electrochemical cell containing a solution of metal ions. The power supply is configured to supply an applied potential to the working electrode, and is operated to supply a voltage of -1 to +1 Volts. An INDEPENDENT CLAIM is included for a method for depositing ultrathin films on nanoparticles.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of components of a cell for synthesis of electrocatalysts.