NOVELTY - A catalyst has a carbon nanostructure coated with an atomically thin shell of a transition metal, and an atomically thin layer of a catalytically active noble metal partially encapsulating the shell.    USE - Catalyst is used in energy conversion device e.g. fuel cell, battery, capacitor and supercapacitor (claimed).    ADVANTAGE - The catalytically active surface layer is smoothly deposited on carbon nanostructure. The catalyst provides energy conversion device having improved long-term stability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method of depositing conformal metal films on carbon nanostructures. Atomically thin shell of transition metal is deposited by oxidizing surface of carbon nanostructures, creating a dipole at the surface of carbon nanostructures, adsorbing metal ions on surface of the carbon nanostructures, reducing the adsorbed metal ions, and replacing the adsorbed metal ions with primary transition metal which is nobler than the adsorbed metal ions. An atomically thin layer of catalytically active noble metal is deposited on surface of atomically thin shell by depositing layer of secondary transition metal, and replacing the layer of secondary transition metal with metal which is more noble than the secondary transition metal;    (2) supercapacitor having primary and secondary electrodes, each comprising carbon nanostructures coated with atomic layer of noble metal atoms, saturated with electrolyte solution and electrically contacted with current collector, and a separator layer electrically insulating primary electrode from secondary electrode; and    (3) aggregate of carbon nanohorns coated with atomic sub-monolayer, monolayer, or bilayer of ruthenium atoms.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view explaining surface chemical reaction for deposition of monoatomic layer of noble metal.    Carbon (1)    Oxygen (2)    Palladium shell (5)    Palladium cation (6)    Platinum atom (7)