Electrolysis in reduced gravitational environments: current research perspectives and future applications.

Electrochemical energy conversion technologies play a crucial role in space missions, for example, in the Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS). They are also vitally important for future long-term space travel for oxygen, fuel and chemical production, where a re-supply of resources from Earth is not possible. Here, we provide an overview of currently existing electrolytic energy conversion technologies for space applications such as proton exchange membrane (PEM) and alkaline electrolyzer systems. We discuss the governing interfacial processes in these devices influenced by reduced gravitation and provide an outlook on future applications of electrolysis systems in, e.g., in-situ resource utilization (ISRU) technologies. A perspective of computational modelling to predict the impact of the reduced gravitational environment on governing electrochemical processes is also discussed and experimental suggestions to better understand efficiency-impacting processes such as gas bubble formation and detachment in reduced gravitational environments are outlined.

Magnetic phase separation in microgravity.

The absence of strong buoyancy forces severely complicates the management of multiphase flows in microgravity. Different types of space systems, ranging from in-space propulsion to life support, are negatively impacted by this effect. Multiple approaches have been developed to achieve phase separation in microgravity, whereas they usually lack the robustness, efficiency, or stability that is desirable in most applications. Complementary to existing methods, the use of magnetic polarization has been recently proposed to passively induce phase separation in electrolytic cells and other two-phase flow devices. This article illustrates the dia- and paramagnetic phase separation mechanism on MilliQ water, an aqueous MnSO4 solution, lysogeny broth, and olive oil using air bubbles in a series of drop tower experiments. Expressions for the magnetic terminal bubble velocity are derived and validated and several wall-bubble and multi-bubble magnetic interactions are reported. Ultimately, the analysis demonstrates the feasibility of the dia- and paramagnetic phase separation approach, providing a key advancement for the development of future space systems.

Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment.

Photoelectrochemical devices integrate the processes of light absorption, charge separation, and catalysis for chemical synthesis. The monolithic design is interesting for space applications, where weight and volume constraints predominate. Hindered gas bubble desorption and the lack of macroconvection processes in reduced gravitation, however, limit its application in space. Physico-chemical modifications of the electrode surface are required to induce gas bubble desorption and ensure continuous device operation. A detailed investigation of the electrocatalyst nanostructure design for light-assisted hydrogen production in microgravity environment is described. p-InP coated with a rhodium (Rh) electrocatalyst layer fabricated by shadow nanosphere lithography is used as a model device. Rh is deposited via physical vapor deposition (PVD) or photoelectrodeposition through a mask of polystyrene (PS) particles. It is observed that the PS sphere size and electrocatalyst deposition technique alter the electrode surface wettability significantly, controlling hydrogen gas bubble detachment and photocurrent-voltage characteristics. The highest, most stable current density of 37.8 mA cm-2 is achieved by depositing Rh via PVD through 784 nm sized PS particles. The increased hydrophilicity of the photoelectrode results in small gas bubble contact angles and weak frictional forces at the solid-gas interface which cause enhanced gas bubble detachment and enhanced device efficiency.

Experimental Methods for Efficient Solar Hydrogen Production in Microgravity Environment.

Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in microgravity environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in microgravity environment, realized at the Bremen Drop Tower during 9.3 s of free fall.

Efficient solar hydrogen generation in microgravity environment.

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.

Advancing semiconductor-electrocatalyst systems: application of surface transformation films and nanosphere lithography.

Photoelectrochemical (PEC) cells offer the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The pursued design involves technologically advanced III-V semiconductor absorbers coupled via an interfacial film to an electrocatalyst layer. These systems have been prepared by in situ surface transformations in electrochemical environments. High activity nanostructured electrocatalysts are required for an efficiently operating cell, optimized in their optical and electrical properties. We demonstrate that shadow nanosphere lithography (SNL) is an auspicious tool to systematically create three-dimensional electrocatalyst nanostructures on the semiconductor photoelectrode through controlling their morphology and optical properties. First results are demonstrated by means of the photoelectrochemical production of hydrogen on p-type InP photocathodes where hitherto applied photoelectrodeposition and SNL-deposited Rh electrocatalysts are compared based on their J-V and spectroscopic behavior. We show that smaller polystyrene particle masks achieve higher defect nanostructures of rhodium on the photoelectrode which leads to a higher catalytic activity and larger short circuit currents. Structural analyses including HRSEM and the analysis of the photoelectrode surface composition by using photoelectron spectroscopy support and complement the photoelectrochemical observations. The optical performance is further compared to theoretical models of the nanostructured photoelectrodes on light scattering and propagation.

Pain perception in patients with bipolar disorder and schizophrenia.

OBJECTIVE: Pain perception is reported to be altered in patients with depression and schizophrenia. However, few studies have investigated the pain perception in patients with bipolar disorders. We therefore aimed to compare pain sensitivity between patients with bipolar disorder, schizophrenia and controls. METHODS: Study groups consisted of 30 patients with bipolar disorder, and control groups consisted of 27 patients with schizophrenia and 59 healthy subjects. Pain perception was assessed with cold pressor test (CPT) by exposure to ice-water. RESULTS: Patients with schizophrenia had significantly higher pain thresholds (PTh) than patients with bipolar disorder. There were no differences between the PTh of patients with schizophrenia and healthy control subjects. However, patients with bipolar disorder had significantly lower pain tolerance (PT) in the CPT than patients with schizophrenia and corresponding healthy control subjects. CONCLUSIONS: The higher PTh in the schizophrenia group compared with the bipolar group found in this study supports further investigation of a potential difference in the pain perception between patients with schizophrenia and bipolar disorder. Theoretical implications of these findings and possible relevant behavioural and neurochemical mechanisms are discussed.

Open-label study of adjunct modafinil for the treatment of patients with fatigue, sleepiness, and major depression treated with selective serotonin reuptake inhibitors.

Despite the efficacy of selective serotonin reuptake inhibitors (SSRIs) in the treatment of major depression, a significant number of patients show partial or no remission of symptoms. Some evidence suggests that psychostimulant augmentation may be helpful in treating patients with residual symptoms of depression. The efficacy of modafinil in augmenting SSRIs in depressed patients with residual fatigue or excessive daytime sleepiness has yet to be systematically investigated. In a series of 25 patients with major depressive disorder, according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, who showed significant residual symptoms after an adequate SSRI trial (12 wk) and who were evaluated according to the Fatigue Severity Scale (FSS), subjects with scores > or = 4 were given open-label modafinil augmentation for a minimum of an additional 6 wk. Treatment response was assessed prospectively with the FSS, the Epworth Sleepiness Scale (ESS), and the Hamilton Rating Scale for Depression (HAM-D) during the first visit and at the second and sixth weeks. Twenty-one of 25 patients in this series who were treated with modafinil and SSRIs completed the 6-wk augmentation trial. At end-point assessment, all patients showed significant improvement in fatigue and sleepiness in FSS and ESS scores, as well as in HAM-D scores (P<.01). In the second week, 29.4% of patients had a HAM-D score <7, which was defined as remission; this rate was 64.7% in the sixth week. The rate of patients whose HAM-D score dropped by more than 50%, defined as responders to treatment, was 41.1% and 76.4% in the second and sixth weeks, respectively. Results of this preliminary, open-label trial suggest that modafinil may be effective in augmenting ongoing SSRI treatment for a portion of patients with major depression who have residual fatigue and sleepiness. Larger, placebo-controlled trials appear warranted to investigate the clinical efficacy and tolerability of modafinil augmentation of SSRI treatment in these patients.