Efficient solar hydrogen generation in microgravity environment

Abstract

Long-term space missions require extra-terrestrial production of storable, renewable energy. Hydrogen is ascribed a crucial role for transportation, electrical power and oxygen generation. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in microgravity environment, providing an alternative route to existing life support technologies for space travel. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15 mA/cm2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the Rh electrocatalyst using shadow nanosphere lithography. The behaviour of the applied system in terrestrial and microgravity environment is simulated using a kinetic transport model. Differences observed for varied catalyst topography are elucidated, enabling future photoelectrode designs for use in reduced gravity environments.

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

“…135,136 Experimentally, a few studies have addressed this issue. 135,136,137,138,139 For example, the bubble effect on illumination has been studied on TiO2 nanorod arrays where oxygen bubbles increased local photocurrents due to concentration of incident light at the three-phase contact line. 136 As the bubble grows, the area surrounding its phase boundary increases and thus the photocurrent enhancement is reduced.…”

Oscillating Hydrogen Bubbles at Pt Microelectrodes

“…Impressive examples are related to sonoluminescence [2,3] or cavitation phenomena [4][5][6] or even the evolution of CO 2 bubbles in champagne [7]. The growth of hydrogen bubbles in light-driven water splitting [8][9][10] or water electrolyzers is a particularly interesting problem of high practical relevance due to the prominent role of hydrogen in energy storage via power-togas processes [11][12][13][14]. Alkaline water electrolysis is still the most mature and least platinum-consuming technology, albeit one suffering from inadequate efficiency.…”

Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

“…In addition, our method is applicable for investigations on several other gas-in-metal systems, where the gas causes a sufficient change in the optical properties of the pristine metal. Especially for hydrogen storage, hydrogen generation (48), and electrochemical applications, the influence of, e.g., grain boundaries in a huge diversity of material systems is of great interest.…”