A multi-perspective analysis of microclimate dynamics for air-based solar hydrogen production.

Navigating the microclimatic environment for the optimal control of water-from-air devices could be a challenge. An example of such a device is an air-based solar hydrogen production device. Such a device promises the ability for off-grid, easily deployable and modular hydrogen production for on-site consumption. Novel analysis techniques, such as wavelet transform coherence analysis, could assist in better understanding the microclimate in which air-based hydrogen production devices might function. The analysis becomes complicated when a system is evaluated at the microclimatic level, especially when it is considered that the performance of air-based solar hydrogen devices are not only dependent on solar radiation, but also on humidity levels in the air. To get a grasp of the interactions that take place within a microclimatic system, a two-tiered approach is presented. It has been shown that relative humidity and temperature is stratified close to the ground, and that the stratification undergoes an inversion twice per day. A possible link between absolute humidity and wind direction is observed and humidity rallies are identified. Using microclimate monitoring and wavelet transform coherence analysis, an attempt is made to disentangle microclimatic variables by pointing out regions of high coherence and regions of low coherence between different variables. It is furthermore suggested that the propagation direction of a humidification process within the microclimate can be determined by considering the phase angle between relative humidity timeseries at different heights above the ground, using wavelet transform coherence analysis. It has been demonstrated that wavelet transform coherence analysis, in conjunction with a comprehensive microclimate monitoring process, could support the understanding of the complex processes that occur within the microclimatic environment and therefore support the management of water-from-air systems. In this regard a management framework is also presented.

Harvesting Hydrogen Gas from Air Pollutants with an Unbiased Gas Phase Photoelectrochemical Cell.

The concept of an all-gas-phase photoelectrochemical (PEC) cell producing hydrogen gas from volatile organic contaminated gas and light is presented. Without applying any external bias, organic contaminants are degraded and hydrogen gas is produced in separate electrode compartments. The system works most efficiently with organic pollutants in inert carrier gas. In the presence of oxygen, the cell performs less efficiently but still significant photocurrents are generated, showing the cell can be run on organic contaminated air. The purpose of this study is to demonstrate new application opportunities of PEC technology and to encourage further advancement toward PEC remediation of air pollution with the attractive feature of simultaneous energy recovery and pollution abatement.

Monolithic cells for solar fuels.

Hybrid energy generation models based on a variety of alternative energy supply technologies are considered the best way to cope with the depletion of fossil energy resources and to limit global warming. One of the currently missing technologies is the mimic of natural photosynthesis to convert carbon dioxide and water into chemical fuel using sunlight. This idea has been around for decades, but artificial photosynthesis of organic molecules is still far away from providing real-world solutions. The scientific challenge is to perform in an efficient way the multi-electron transfer reactions of water oxidation and carbon dioxide reduction using holes and single electrons generated in an illuminated semiconductor. In this tutorial review the design of photoelectrochemical (PEC) cells that combine solar water oxidation and CO2 reduction is discussed. In such PEC cells simultaneous transport and efficient use of light, electrons, protons and molecules has to be managed. It is explained how efficiency can be gained by compartmentalisation of the water oxidation and CO2 reduction processes by proton exchange membranes, and monolithic concepts of artificial leaves and solar membranes are presented. Besides transferring protons from the anode to the cathode compartment the membrane serves as a molecular barrier material to prevent cross-over of oxygen and fuel molecules. Innovative nano-organized multimaterials will be needed to realise practical artificial photosynthesis devices. This review provides an overview of synthesis techniques which could be used to realise monolithic multifunctional membrane-electrode assemblies, such as Layer-by-Layer (LbL) deposition, Atomic Layer Deposition (ALD), and porous silicon (porSi) engineering. Advances in modelling approaches, electrochemical techniques and in situ spectroscopies to characterise overall PEC cell performance are discussed.