Cost-effective design of the alkaline electrolyser for enhanced electrochemical performance and reduced electrode degradation

An alkaline electrolyser was developed and characterized. Three different metals, working as the electrode, were analysed using electrochemical methods to determine the best electrochemical performance. The performance of the Stainless Steel (SS316) electrode and the nickel electrode is much better than that of the conventional iron electrode. Degradation analysis of the electrode materials highlighted the need for the material to be durable and resistant to corrosion from an alkaline environment. Through SEM and mass analysis, it is shown that Nickel exhibits the strongest long-term resistance to surface and electrochemical performance degradation, when compared with Mild Steel (Iron) and SS316

Feasibility of an oxygen-getter with nickel electrodes in alkaline electrolysers

Alkaline electrolysis is the long-established technology for water splitting to produce hydrogen and has been industrially used since the nineteenth century. The most common materials used for the electrodes are nickel and derivatives of nickel (e.g. Raney nickel). Nickel represents a cost-effective electrode material due to its low cost (compared to platinum group metals), good electrical conductivity and exhibits good resistance to corrosive solutions. The steady degradation of the nickel electrodes over time is known as a result of oxide layer formation on the electrode surface. Reducing oxide layer growth on the electrode surface will increase the efficiency and lifetime of the electrolyser. Titanium has a higher affinity to oxygen than nickel so has been introduced to the electrolyser as a sacrificial metal to reduce oxide layer formation on the nickel. Two identical electrolysers were tested with one difference: Cell B had titanium chips present in the electrolyte solution, whilst Cell A did not have titanium present. SEM results show a reduction of 16 % in the thickness of the Cell B oxide layer on nickel compared to the Cell A nickel, which is supported by the large increase in oxide layer build-up on the titanium in Cell B. EDX on the same samples showed on average a 59 % decrease in oxygen on the Cell B nickel compared to Cell A. XPS surface analysis of the same samples showed a 17 % decrease in the oxygen on Cell B nickel. These results support the hypothesis that adding titanium to an alkaline electrolyser system with nickel electrodes can reduce the oxide layer formation on the nickel

Assessment of Iron(III) chloride as a catalyst for the production of hydrogen from the supercritical water gasification of microalgae

Alkali metal salts and supported transition metals have been the dominant catalysts used to maximise hydrogen production from supercritical water gasification (SCWG). Recently, FeCl3 has emerged as an alternative to these that has been found to be more effective in some cases reported in literature. However, to these authors’ knowledge, few studies exist that study this catalyst with none that involve microalgae as the feedstock. Investigation is reported into the effect of FeCl3 on the SCWG of Chlorella vulgaris for a range of temperatures (400–600°C) and biomass concentrations (1–3wt%), with comparisons made to other catalysts (KOH, Ru/C and their combinations). A significant decrease in hydrogen yield, carbon conversion and energy efficiency was observed with the addition of FeCl3, due to a reduced pH which suppressed the water gas shift reaction and catalysed of char forming reactions. This was in contrary to Ru/C and KOH catalysts, where those outcomes increased. Additionally, when FeCl3 was used with Ru/C, the ruthenium was poisoned, nullifying its positive effects. Consequently, FeCl3 is not a suitable catalyst for hydrogen production from microalgae, either alone or in conjunction with a ruthenium catalyst

Heat storage performance analysis and parameter design for encapsulated phase change materials

This paper establishes a thermo-mechanical model considering the liquid density variation to explore the comprehensive energy storage performance of two types of small-sized encapsulated phase change materials (PCMs) as well as effects of shell thickness. The study shows that the varying ranges of internal pressure, melting temperature and latent heat are markedly diminished during melting of PCMs after taking into account the liquid density variation. The decrease of shell thickness leads to a decrease of maximum internal pressure and a larger decrease of critical cracking pressure, which will increase the risk of shell cracking. The decrease in shell thickness slows down the increase in melting temperature and the decrease in latent heat during the melting process, which consequently reduces the melting time and increases the stored latent energy. These results indicate that reducing shell thickness of encapsulated PCMs is favourable for elevating energy charging rate and energy storage capacity while it is harmful to mechanical stability. The Cu/Ni capsule has smaller critical core/shell size ratio to avoid cracking than the salts/SiC capsule, while the former offers a shorter melting period. This implies that physical properties of materials of PCM capsules should be carefully considered for improving mechanical stability and melting dynamics. This study is helpful for selection of appropriate shell thickness and materials to achieve excellent comprehensive energy storage performance of encapsulated PCMs

Design for On-Site Hydrogen Production for Hydrogen Fuel Cell Vehicle Refueling Station at University of Birmingham, U.K.

In April 2008, the University of Birmingham launched the first permanent Hydrogen Refuelling Station in the UK. This enabled the refuelling of the only at the time fleet of Hydrogen Hybrid Fuel Cell Vehicles (HHFCV) in the UK. To maintain the low emissions ethos, the ultra-high purity “Green” hydrogen for the refuelling station was supplied off site, from a third party contractor. The University aims to be the first campus in the UK that is carbon neutral and this project scopes to produce “Green” hydrogen on-site to power the fleet of HHFCVs. Electrolysis is currently the only commercial method for producing ultra-high purity hydrogen without the need for, what could prove to be very costly, additional purification steps. Working in collaboration with ITM Power, a HPac Model electrolyser has been installed to produce electrolytic hydrogen on-site (up to 1.25 kgH2/day). The HPac uses PEM technology, which eliminates the need for hazardous alkaline substances, to produce hydrogen. The input requirements are ASTM Type 2 de-ionised (DI), water and 240 V power supply. Hydrogen is produced at pressures up to 15 bar [1]. However, there is a need to incorporate this unit within the existing hydrogen infrastructure incorporating 350 bar Air Product refuelling station. An integrated delivery system has been designed and initial results are presented herein

Analysis of the Supercritical Water Gasification of Cellulose in a Continuous System Using Short Residence Times

Supercritical Water Gasification (SCWG) has the capacity to generate fuel gas effluent from wet biomass without previously having to dry the biomass. However, substantial efforts are still required to make it a feasible and competitive technology for hydrogen production. Biomass contains cellulose, hemicellulose and lignin, so it is essential to understand their behavior in high-pressure systems in order to optimize hydrogen production. As the main component of biomass, cellulose has been extensively studied, and its decomposition has been carried out at both subcritical and supercritical conditions. Most previous works of this model compound were carried out in batch reactors, where reaction times normally take place in a few minutes. However, the present study demonstrates that gasification reactions can achieve efficiency levels of up to 100% in less than ten seconds. The effect of temperature (450-560 degrees C), the amount of oxidant (from no addition of oxidant to an excess over stoichiometric of 10%, n = 1.1), the initial concentration of organic matter (0.25-2 wt.%) and the addition of a catalyst on the SCWG of cellulose in a continuous tubular reactor at short residence times (from 6 to 10 s) have been studied in this work. Hydrogen yields close to 100% in the gas phase were obtained when operating under optimal conditions. Moreover, a validation of the experimental data has been conducted based on the theoretical data obtained from its kinetics

Thermo-mechanical analysis of microcapsules containing phase change materials for cold storage

This is an accepted manuscript of an article published by Elsevier in Applied Energy on 18/12/2017, available online: https://doi.org/10.1016/j.apenergy.2017.12.021 The accepted version of the publication may differ from the final published version.Microencapsulated phase change material slurries (MEPCMSs) offer a potentially efficient and flexible solution for cryogenic-temperature cold storage. In this paper, the phase change material (PCM) microcapsules prepared to form MEPCMSs for cryogenic-temperature cold storage consist of Dowtherm J (DJ) as core material and melamine formaldehyde (MF) as primary shell material. DJ is an aromatic mixture with diethylbenzene as the main component. Composite shell materials are adopted to avoid cracking by adding aluminium oxide (Al2O3) nanoparticles or copper (Cu) coating into/on MF shell. In order to explore the heat transfer behaviour and mechanical stability of the microcapsules during the solidification process of PCM, a thermo-mechanical model is established by taking into account of energy conservation, pressure-dependent solid-liquid equilibria, Lamé’s equations and buckling theory. Based on the proposed model, the effects of shell thickness, shell compositions and microcapsule size are therefore studied on the variations of pressure difference, freezing point, and latent heat. The cause of shell deformation is clearly explained and the shell buckling modes are predicted using the model, which agree well with the experimental observations. The critical core/shell size ratios of avoiding buckling are proposed for the microcapsules with different compositions. Simultaneously incorporation of Al2O3 nanoparticles and Cu coating into/on MF shell can markedly enhance the resistant to buckling. In addition, special attention is paid to cold energy storage capacity of MEPCMSs, which has considerable superiority compared to packed pebble beds

Adsorption of carbon dioxide on hydrotalcite-like compounds of different compositions

The adsorption of carbon dioxide on hydrotalcite-like compounds was investigated. Two different powdered hydrotalcites were used containing the cations nickel and iron. The powdered materials were screened for carbon dioxide adsorption using a thermogravimetric method and it was found that NiMgAl (Sample 1) hydrotalcite has the largest capacity for CO2, adsorbing 1.58 mmol g−1 at 20 °C, and highest rate of adsorption of up to 0.17 mmol g−1 min−1. This represented an increase of 53% in adsorption capacity, compared with NiMgAlFe (Sample 2). In order to improve the rheological behaviour of hydrotalcite paste for extrusion, hydrotalcite powders were combined with boehmite alumina (70:30 and 50:50 ratios of hydrotalcite:boehmite) before extrusion into pellets suitable for use in a fixed bed adsorber. These pellets were then re-crushed and further tested by thermogravimetric methods. The effects of temperature, composition and pre-treatment of the hydrotalcites on the adsorption of carbon dioxide and nitrogen are reported. At 20 °C, the amount of carbon dioxide adsorbed was between 2.0 and 2.5 mmol g−1 for all the hydrotalcite/alumina samples in this study, although this decayed rapidly with increasing temperature. The results are compared with silica gel as a common sorbent reference, and with literature values. Hydrotalcite/alumina samples have thermal stability and a high adsorption capacity for carbon dioxide over a wide range of temperatures. The composition of the hydrotalcite/alumina pellets investigated in this study has less effect upon the adsorption behaviour compared with the non-calcined hydrotalcite powder, thus allowing a wide choice of pellet compositions to be used