Production & Supply Chain

This paper presents a novel system design that considerably improves the entrapment of terrestrial ultraviolet (UV) irradiance in a customized honeycomb structure to produce hydrogen at a standard rate of 7.57 slpm for places with a UV index > 11. Thermolysis of high salinity water is done by employing a solid oxide electrolyzer cell (SOEC) which comprises three customized novel active optical subsystems to filter track and concentrate terrestrial UV solar irradiance by Fresnel lenses. The output of systems is fed to a desalinator a photovoltaic system to produce electrical energy and a steam generator with modified surface morphology to generate the required superheated steam for the SOEC. A simulation in COMSOL Multiphysics ver. 5.6 has shown that a customized honeycomb structure when incorporated on the copper–nickel surface of a steam generator improves its absorptance coefficient up to 93.43% (48.98%—flat case). This results in generating the required superheated steam of 650 ◦C with a designed active optical system comprising nine Fresnel lenses (7 m2 ) that offer the concentration of 36 suns on the honeycomb structure of the steam generator as input. The required 1.27 kW of electrical power is obtained by concentrating the photovoltaic system using In0.33Ga0.67N/Si/InN solar cells. This production of hydrogen is sustainable and cost effective as the estimated cost over 5 years by the proposed system is 0.51 USD/kg compared to the commercially available system which costs 3.18 USD/kg.

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean complex-chemistry hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach for evaluating mean species concentrations. For this purpose dependencies of mole fractions and rates of production of various species on a combustion progress variable c obtained from the laminar flame are averaged adopting either the actual Probability Density Function (PDF) P (c)  extracted from the DNS data or a common presumed β-function PDF. On the one hand the results quantitatively validate the flamelet approach for the mean mole fractions of all species including radicals but only if the actual PDF P (c) is adopted. The use of the β-function PDF yields substantially worse results for the radicals’ concentrations. These findings put modeling the PDF P (c) on the forefront of the research agenda. On the other hand the mean rate of product creation and turbulent burning velocity are poorly predicted even adopting the actual PDF. These results imply that in order to evaluate the mean species concentrations the flamelet approach could be coupled with another model that predicts the mean rate and turbulent burning velocity better. Accordingly the flamelet approach could be implemented as post-processing of numerical data yielded by that model. Based on the aforementioned findings and implications a new approach to building a presumed PDF is developed. The key features of the approach consist in (i) adopting a re-normalized flamelet PDF for intermediate values of c and (ii) directly using the mean rate of product creation to calibrate the presumed PDF. Capabilities of the newly developed PDF for predicting mean species concentrations are quantitively validated for all species including radicals.

From a permeability and selectivity perspective supported thin-film Pd–Ag membranes are the best candidates for high-purity hydrogen recovery for methane-hydrogen mixtures from the natural gas grid. However the high hydrogen flux also results in induced bulk-to-membrane mass transfer limitations (concentration polarization) especially when working at low hydrogen concentration and high pressure which further reduces the hydrogen permeance in the presence of mixtures. Additionally Pd is a precious metal and its price is lately increasing dramatically. The use of inexpensive CMSM could become a promising alternative. In this manuscript a detailed comparison between these two membrane technologies operating under the same working pressure and mixtures is presented.<br/>First the permeation properties of CMSM and Pd–Ag membranes are compared in terms of permeance and purity and subsequently making use of this experimental investigation an economic evaluation including capital and variable costs has been performed for a separation system to recover 25 kg/day of hydrogen from a methane-hydrogen mixture. To widen the perspective also a sensitivity analysis by changing the pressure difference membrane lifetime membrane support cost and cost of Pd/Ag membrane recovery has been considered. The results show that at high pressure the use of CMSM is to more economic than the Pd-based membranes at the same recovery and similar purity.

Chemical looping water splitting or chemical looping hydrogen is a very promising technology for the production of hydrogen. In recent years extensive research has enabled remarkable leaps towards a successful integration of the chemical looping technology into a future hydrogen infrastructure. Progress has been reported with iron based oxygen carriers for stable hydrogen production capacity over consecutive cycles without significant signs of degradation. The high stability improvements were achieved by adding alien metal oxides or by integrating the active component into a mineral structure which offers excellent resistance towards thermal stress. Prototype systems from small μ-systems up to 50 kW have been operated with promising results. The chemical looping water splitting process was broadened in terms of its application area and utilization of feedstocks using a variety of renewable and fossil resources. The three-reactor system was clearly advantageous due to its flexibility heat integration capabilities and possibility to produce separate pure streams of hydrogen CO₂ and N₂. However two-reactor and single fixed-bed reactor systems were successfully operated as well. This review aims to survey the recently presented literature in detail and systematically summarize the gathered data.

Ferrosilicon 75 a 50:50 mixture of silicon and iron disilicide has been activated toward hydrogen generation by processing using ball milling allowing a much lower concentration of sodium hydroxide (2 wt %) to be used to generate hydrogen from the silicon in ferrosilicon with a shorter induction time than has been reported previously. An activation energy of 62 kJ/mol was determined for the reaction of ball-milled ferrosilicon powder with sodium hydroxide solution which is around 30 kJ/mol lower than that previously reported for unmilled ferrosilicon. A series of composite powders were also prepared by ball milling ferrosilicon with various additives in order to improve the hydrogen generation properties from ferrosilicon 75 and attempt to activate the silicon in the passivating FeSi2 component. Three different classes of additives were employed: salts polymers and sugars. The effects of these additives on hydrogen generation from the reaction of ferrosilicon with 2 wt% aqueous sodium hydroxide were investigated. It was found that composites formed of ferrosilicon and sodium chloride potassium chloride sodium polyacrylate sodium polystyrene sulfonate-co-maleic acid or fructose showed reduced induction times for hydrogen generation compared to that observed for ferrosilicon alone and all but fructose also led to an increase in the maximum hydrogen generation rate. In light of its low cost and toxicity and beneficial effects sodium chloride is considered to be the most effective of these additives for activating the silicon in ferrosilicon toward hydrogen generation. Materials characterisation showed that neither ball milling on its own nor use of additives was successful in activating the FeSi2 component of ferrosilicon for hydrogen generation and the improvement in rate and shortening of the induction period was attributed to the silicon component of the mixture alone The gravimetric storage capacity for hydrogen in ferrosilicon 75 is therefore maintained at only 3.5% rather than the 10.5% ideally expected for a material containing 75% silicon. In light of these results ferrosilicon 75 does not appear a good candidate for hydrogen production in portable applications.

In this work CdS/SiC/TiO₂ tri-composite photocatalysts that exploit electron- and hole-transfer processes were fabricated using an easy two-step method in the liquid phase. The photocatalyst with a 1:1:1 M ratio of CdS/SiC/TiO₂ exhibited a rate of hydrogen evolution from an aqueous solution of sodium sulfite and sodium sulfide under visible light of 137 μmol h⁻¹ g⁻¹ which is 9.5 times that of pure CdS. β-SiC can act as a sink for the photogenerated holes because the valence band level of β-SiC is higher than the corresponding bands in CdS and TiO2. In addition the level of the conduction band of TiO2 is lower than those of CdS and β-SiC so TiO₂ can act as the acceptor of the photogenerated electrons. Our results demonstrate that hole transfer and absorption in the visible light region lead to an effective hydrogen-production scheme.

Using a high mass transport floating electrode technique with an ultra-low catalyst loading (0.84–3.5 μgPt cm−2) of commonly used Pt/C catalyst (HiSPEC 9100 Johnson Matthey) features in the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) were resolved and defined which have rarely been previously observed. These features include fine structure in the hydrogen adsorption region between 0.18 < V vs. RHE < 0.36 V vs. RHE consisting of two peaks an asymptotic decrease at potentials greater than 0.36 V vs. RHE and a hysteresis above 0.1 V vs. RHE which corresponded to a decrease in the cathodic scan current by up to 50% of the anodic scan. These features are examined as a function of hydrogen and proton concentration anion type and concentration potential scan limit and temperature. We provide an analytical solution to the Heyrovsky–Volmer equation and use it to analyse our results. Using this model we are able to extract catalytic properties (without mass transport corrections; a possible source of error) by simultaneously fitting the model to HOR curves in a variety of conditions including temperature hydrogen partial pressure and anion/H+ concentration. Using our model we are able to rationalise the pH and hydrogen concentration dependence of the hydrogen reaction. This model may be useful in application to fuel cell and electrolyser simulation studies.

Plasmonic Ni nanoparticles were incorporated into LaFeO₃ photocathode (LFO-Ni) to excite the surface plasmon resonances (SPR) for enhanced light harvesting for enhancing the photoelectrochemical (PEC) hydrogen evolution reaction. The nanostructured LFO photocathode was prepared by spray pyrolysis method and Ni nanoparticles were incorporated on to the photocathode by spin coating technique. The LFO-Ni photocathode demonstrated strong optical absorption and higher current density where the untreated LFO film exhibited a maximum photocurrent of 0.036 mA/cm² at 0.6 V vs RHE and when incorporating 2.84 mmol Ni nanoparticles the photocurrent density reached a maximum of 0.066 mA/cm² at 0.6 V vs RHE due to the SPR effect. This subsequently led to enhanced hydrogen production where more than double (2.64 times) the amount of hydrogen was generated compared to the untreated LFO photocathode. Ni nanoparticles were modelled using Finite Difference Time Domain (FDTD) analysis and the results showed optimal particle size in the range of 70–100 nm for Surface Plasmon Resonance (SPR) enhancement.

A key challenge for future clean power or hydrogen projects via gasification is the need to reduce the overall cost while achieving significant levels of CO2 capture. The current state of the art technology for capturing CO2 from sour syngas uses a physical solvent absorption process (acid gas removal–AGR) such as Selexol™ or Rectisol® to selectively separate H2S and CO2 from the H2. These two processes are expensive and require significant utility consumption during operation which only escalates with increasing levels of CO2 capture. Importantly Air Products has developed an alternative option that can achieve a higher level of CO2 capture than the conventional technologies at significantly lower capital and operating costs. Overall the system is expected to reduce the cost of CO2 capture by over 25%.<br/>Air Products developed this novel technology by leveraging years of experience in the design and operation of H2 pressure swing adsorption (PSA) systems in its numerous steam methane reformers. Commercial PSAs typically operate on clean syngas and thus need an upstream AGR unit to operate in a gasification process. Air Products recognized that a H2 PSA technology adapted to handle sour feedgas (Sour PSA) would enable a new and enhanced improvement to a gasification system. The complete Air Products CO2 Capture technology (CCT) for sour syngas consists of a Sour PSA unit followed by a low-BTU sour oxycombustion unit and finally a CO2 purification / compression system.

Fossil fuels have to be substituted by climate neutral fuels to contribute to CO₂ reduction in the future energy system. Pyrolysis of natural gas is a well-known technical process applied for production of e. g. carbon black.

In the future it might contribute to carbon dioxide-free hydrogen production. Production of hydrogen from natural gas pyrolysis has thus gained interest in research and energy technology in the near past. If the carbon by-product of this process can be used for material production or can be sequestrated the produced hydrogen has a low carbon footprint.

This article reviews literature on the state of the art of methane/ natural gas pyrolysis process developments and at-tempts to assess the technology readiness level (TRL).