Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

TL;DR

This study demonstrates that near-infrared pulsed laser irradiation of colloidal gold nanoparticle solutions can generate molecular hydrogen through plasma-induced water splitting, with emission rates depending on laser energy and type of solvent.

Contribution

It introduces a novel, electrode- and photocatalyst-free method for hydrogen production using laser-induced plasma in colloidal solutions of nanoparticles.

Findings

Hydrogen emission depends on laser pulse energy and has a threshold fluence.

H2 emission is higher in ethanol than in water colloids.

Laser exposure can induce plasma and hydrogen emission in pure liquids.

Abstract

We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of plasma of laser breakdown of liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50 J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.