Flashlight-Induced Explosive Chemical Reaction for Fabrication of Flameproof Nickel Electrode

In this study, a unique method is proposed for the fabrication of a high-temperature-operable nickel electrode from nickel hydrazine nitrate (NHN), an explosive substance, using flashlight irradiation. NHN was synthesized by a simple mixing of nickel nitrate and hydrazine in an aqueous solution. When NHN was illuminated by a flashlight (energy density: 6 J/cm², wavelength: 350–1000 nm, exposure time: 6 ms), it absorbed the light energy and decomposed partially, initiating an explosive chemical reaction with the gas. The temperature of NHN increased instantaneously, causing a local explosive reaction on the surface of the NHN film. The explosion reaction induced a continuous conversion of the NHN film to metallic nickel, resulting in the fabrication of a conductive nickel electrode. The fabricated nickel electrode showed an excellent conductivity (5.1 Ω, 1.2177 Ω/□ and 0.0244 Ω∙cm) and a higher thermal-oxidation resistance (13.7 Ω after the reaction at 400 °C for 30 min) than the conventional copper nanoparticle-based electrode (5 MΩ after the reaction at 250 °C for 30 min). Further, the nickel electrode, as a Joule heater, exhibited a temperature increment of 200 °C at 2.0 V. The applicability of nickel electrodes as a flameproof electrode was simply demonstrated by illuminating a LED bulb at 450 °C. Nickel-based high-temperature electronics was demonstrated by lighting an LED bulb for 60 min. This study demonstrates an advanced technique, that is, the use of the intensive pulse light (IPL) or flashlight to control explosive chemical reactions, which is a significant improvement over the conventional sintering process.