A mercury-based compound is in powder form and has the general chemical formula: M1.sub.aX.sub.b, where M1 is Hg, MxcMyd or a combination thereof, with Mx being Hg and My being an arbitrary element; wherein X is chloride, bromide, fluoride, iodide, sulphate, nitrate or a combination thereof, wherein a, b, c, and d are numbers between 0.1 and 10, wherein particles of the powder have a minimum average dimension of width of at least 50 nm and a maximum average dimension of width of at most 20 m, and wherein the mercury-based compound is paramagnetic and is present in an excited state.

A perovskite with a formula LaMn.sub.xRu.sub.yNi.sub.1(x+y)O.sub.3 is disclosed, where x is from 0.02 to 0.08 and y is from 0.08 to 0.02. The perovskite has a morphology of spherical particles with an oxidation state of Mn and Ru both as +3. The perovskite can be used as a coating on the electrode. The resulting perovskite-coated electrode exhibits excellent electrochemical properties in an asymmetric supercapacitor, proving that the perovskite is an ideal electrode material.

Provided is a method of producing a metal nanoparticle-oxide support complex structure, in which metal nanoparticles uniform in size are evenly distributed on the surface of oxide supports. A gas sensor with improved gas sensing ability and durability may be provided by using the same.