Search

This work provides an overview of R&D activities at South African Institute for Advanced Materials Chemistry (SAIAMC) on metal hydride hydrogen compression technology with a focus on engineering solutions for industrial-scale applications. A summary of layout features, as well as test / operation results are presented for industrial-scale prototypes of: (i) 1-stage H2 compressor for refueling station (50–200 bar, up to 13 Nm3/h), and (ii) 3-stage H2 compressor (3–200 bar, up to 5 Nm3/h). The developed systems provide hydrogen compression utilizing low-grade steam (T=120–140 °C) and cooling water (T=15–25 °C) available at sites of industrial customers.

TiH2-modified MgH2 was prepared by high energy reactive ball milling (HRBM) of Mg and Ti in hydrogen and showed high weight H storage capacity and fast hydrogenation/dehydrogenation kinetics. However, a decrease in the reversible H storage capacity on cycling at high temperatures takes place and is a major obstacle for its use in hydrogen and heat storage applications. Reversible hydrogen absorption/desorption cycling of the materials requires use of the working temperature ≥330 °C and results in a partial step-by-step loss of the recoverable hydrogen storage capacity, with less significant changes in the rates of hydrogenation/dehydrogenation. After hydrogen desorption at 330–350 °C, hydrogen absorption can proceed at much lower temperatures, down to 24 °C. However, a significant decay in the reversible hydrogen capacity takes place with increasing number of cycles. The observed deterioration is caused by cycling-induced drastic morphological changes in the studied composite material leading to a segregation of TiH2 particles in the cycled samples instead of their initial homogeneous distribution. However, the introduction of 5 wt% of graphite into the MgH2–TiH2 composite system prepared by HRBM leads to an outstanding improvement of the hydrogen storage performance. Indeed, hydrogen absorption and desorption characteristics remain stable through 100 hydrogen absorption/desorption cycles and are related to an effect of the added graphite. The TEM study showed that carbon is uniformly distributed between the MgH2 grains covering segregated TiH2, preventing the grain growth and thus keeping the reversible storage capacity and the rates of hydrogen charge and discharge unchanged. Modelling of the kinetics of hydrogen absorption and desorption in the Mg–Ti and Mg–Ti–C composites showed that the reaction mechanisms significantly change depending on the presence or absence of graphite, the number of absorption–desorption cycles and the operating temperature.

A range of AB2-type (A=Ti+Zr, B=Cr+Mn+Ni+Fe+V) intermetallic alloys were investigated for both hydrogen storage and compression applications as the manufacturing process was scaled up from laboratory scale (50-100g) to industrial scale (∼10 kg) using the vacuum induction melting process. In the produced alloys the hydrogen sorption properties were modified by tuning the component composition through varying the Zr content on the A side, along with the content of V and Cr on the B side. It was shown that successful tuning of the hydrogen sorption properties of AB2-type materials can be achieved by the variation of the component composition, relating to the contents of Zr, V and Cr. At a fixed, quite low Zr/(Ti+Zr) ratio the PCT properties of the materials can be adjusted in wide limits by the variation of V content which, in addition, results in the increase of the hydrogen storage capacity.

Proton exchange membrane fuel cells (PEMFCs) allow producing the energy in clean and efficient way using hydrogen. They are being used in a variety of applications which characterize better performance. High temperature PEMFC (HT-PEMFC) technology is being developed as it exhibits advantages over low temperature PEMFC (LT-PEMFC). Though, the commercialization of HT-PEMFCs is still hampered because of performance degradation and limited life time. The performance of HT-membrane electrode assemblies (HT-MEAs) is affected because of various degradation mechanisms occurring during operation, like membrane thinning, phosphoric acid leaching, electrode carbon support corrosion, which causes the loss of electrochemically active surface area (ECSA) of platinum catalyst due to platinum particle agglomeration. The aim of this work is to study electrode carbon corrosion under accelerated stress test (AST) conditions. Carbon corrosion is influenced by temperature, relative humidity, open-circuit voltage (OCV), cell potential, start stop cycling and also fuel starvation. The influence of OCV and higher cell voltages on carbon corrosion is studied in phosphoric acid doped polybenzimidazole (PBI) based HT-MEA of 100 cm2 active area. The carbon corrosion is assessed using IR spectroscopy by detecting the carbon dioxide gas in cathode exhaust during 30 minutes operation at AST conditions. 63.55 µg.cm-2 of carbon is lost as carbon dioxide after the 1.2 V potential test. In-situ performance deterioration is observed using electrochemical methods like polarisation curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Impedance studies showed no change in membrane resistance whereas cathode polarisation losses increased after the AST. TEM analysis shows that the platinum particle size is increased after the operation at 1.2 V potential test. The ECSA of HT-MEA decreased over the time due to operation at various AST conditions which affected the fuel cell performance. The ECSA decreased from 20.06 m2.g-1 to 15.43 m2.g-1 of Pt after the 1.2 V applied potential test.

Proton exchange membrane fuel cells (PEMFC) not only offer more efficient electrical energy conversion, relative to on-ground/backup turbines but generate by-products useful in aircraft such as heat for ice prevention, deoxygenated air for fire retardation and drinkable water for use on-board. Consequently, several projects (e.g. DLR-H2 Antares and RAPID2000) have successfully tested PEMFC-powered auxiliary unit (APU) for manned/unmanned aircraft. Despite the progress from flying PEMFC-powered small aircraft with 20 kW power output as high as 1 000 m at 100 km/h to 33 kW at 2 558 m, 176 km/h [1, 2, 3], durability and reliability remain key challenges. This review reports on the inadequate understanding of behaviour of PEMFC under aeronautic conditions and the lack of predictive methods conducive for aircraft that provide real-time information on the State of Health of PEMFCs.Highlights: The main research findings are–To minimize performance loss due to high altitude and inclination by adjusting cathode stoichiometric ratio.–To improve quality of oxygen-depleted air by controlling operating temperature and stoichiometric ratio.–Need to devise real time prediction methods conducive for determining PEMFC SoH in aircraft.

This paper reviews state-of-the art developments in hydrogen energy systems which integrate fuel cells with metal hydride-based hydrogen storage. The 187 reference papers included in this review provide an overview of all major publications in the field, as well as recent work by several of the authors of the review. The review contains four parts. The first part gives an overview of the existing types of fuel cells and outlines the potential of using metal hydride stores as a source of hydrogen fuel. The second part of the review considers the suitability and optimisation of different metal hydrides based on their energy efficient thermal integration with fuel cells. The performances of metal hydrides are considered from the viewpoint of the reversible heat driven interaction of the metal hydrides with gaseous H2. Efficiencies of hydrogen and heat exchange in hydrogen stores to control H2 charge/discharge flow rates are the focus of the third section of the review and are considered together with metal hydride – fuel cell system integration issues and the corresponding engineering solutions. Finally, the last section of the review describes specific hydrogen- fuelled systems presented in the available reference data.

In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its gas diffusion electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors gas transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm−2, and a maximum power density of 0.54 W cm−2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPL-free GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications.

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) have received substantial attention in stationary sector applications, due to their high carbon monoxide (CO) tolerance, high-quality waste heat and simplified water management system. Hydrogen rich gas produced in a fuel reforming process can be used and can be directly supplied to the HT-PEMFC stack anode omitting complex hydrogen purification process. It allows a wide range of fuel flexibility for the reforming process. The present study is an analysis of HT-PEMFC stack performance operating with an integrated steam reformer, operated with various fuels like ethanol, glycerol, methanol, methane and other fuels. The HT-PEMFC stack is modelled with a concept of varying local current density in the cathode catalyst layer.

This paper describes a Portable Polymer Electrolyte Membrane Fuel Cell (PEMFC) System developed at HySA Systems, UWC. The system has a rated maximum output power of 130 W at 240 VAC and 5 VDC USB output port. Hydrogen is supplied to the PEMFC using Metal Hydride (MH) on the basis of a multi-component AB2 – type hydrogen storage alloy (A=Ti,Zr; B=Mn,Fe,Cr,Ni; Ti:Zr=0.55:0.45). The stainless steel MH canister with external aluminium fins was developed in-house. The heat transfer performance was optimized by utilizing external fins and compacting thermal expanded graphite (TEG) with the MH powder to form pellets. The MH canister has a maximum hydrogen storage capacity of 90 NL H2. It is well-known that the endothermic desorption of H2 from MH results in the significant cooling, which decrease H2 supply flow rate. To overcome this problem and improve the dynamic performance, the MH canister was placed in front of the fuel cell exhaust to utilise the waste heat generated by PEMFC. By utilisation of the PEMFC waste heat in combination with external fins and MH / TEG compacts, the MH canister allowed for >40 minutes-long stable operation at the stack power of 130 W (225 W/kg(MH)) with the utilisation of >90% of the stored H2. Figure 1 illustrates the MH storage unit integrated with 200 W PEMFC stack, Figure 2 shows the rated power of the PEMFC and temperature of the MH canister at different loads connected to the system. Figure 1

A novel hydrogen storage system for a RX60-30L 3-tonne electric forklift (STILL), equipped with a GenDrive 1600-80A fuel cell power module (Plug Power) has been developed. The system combines a compressed H2 composite cylinder (CGH2) and a liquid-heated-cooled metal hydride (MH) extension tank which is thermally integrated with a power module. The MH extension tank comprises a MH bed formed according to an advanced solution to provide easy activation of the MH material and fast H2 charge/discharge. The system has the same hydrogen storage capacity (∼19 Nm3 H2 or 1.7 kg) as the separate CGH2 tank charged at P = 350 bar, but at a lower H2 charge pressure (≤185 bar). A 15 min cycle refuelling provides the forklift with full-load operation (according to VDI-60 protocol) during >3 h, or 2 to 4 working shifts in a real industrial environment. The work also presents a hydrogen refuelling station (dispensing pressure up to 185 bar) with integrated MH compressor which has been developed for forklift refuelling.

Pt3M (M: Co, Ni and Fe) bimetallic alloy nanoclusters were synthesized by a novel and simple chemical reduction approach, and employed as the promising electrocatalyst to accelerate the kinetics of oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells. From XRD, the positive shift of diffraction angle confirms the alloy formation between Pt and M and the elemental composition was confirmed by energy dispersive X-ray spectroscopy analysis. The nanocluster morphology and particle size was determined using scanning and transmission electron microscopy analysis. The ORR kinetic parameters for Pt-M electrocatalysts were calculated and compared with reported Pt/C catalysts. Among the Pt-M electrocatalysts, Pt-Co was found to be the most efficient catalyst having the higher mass and specific activity (at 0.9 V vs. RHE) of 0.44 mA/μg and 0.69 mA/cm2, respectively. The accelerated durability test reveals that the Pt-M bimetallic alloy nanoclusters retain appreciable surface area and mass activity after 8000 potential cycles confirms good long-term durability, and also competing with the reported benchmark ORR catalysts.

We present test results of a commercial 3-tonne electric forklift (STILL) equipped with a commercial fuel cell power module (Plug Power) and a MH hydrogen storage tank (HySA Systems and TF Design). The tests included: (i) performance evaluation of “hybrid” hydrogen storage system during refuelling at low (

In [1, 2] we reported about development of metal hydride (MH) extension tank for fuel cell powered forklift, along with H2 refuelling station with integrated MH compressor. An overview of the MH compressors developed at SAIAMC and HySA Systems can be found in [3]. Here, we present the details about layout and operation of the H2 refuelling station at Impala Platinum refineries in Springs, South Africa, since its start-up in October 2015 (officially launched on March 31, 2016). The station provides H2 dispensing at the pressure up to 185 bar and uses pipeline H2 (P~50 bar) available at the customer site. H2 compression to P=200 bar with productivity up to 13 Nm3/h is provided by the integrated 1-stage metal hydride (MH) H2 compressor which uses steam (T~130 °C) for the heating and circulating water (T~20 °C) for the cooling ; both steam and water are also available from the customer infrastructure. The station also includes H2 dispenser, buffer tank (standard gas cylinder pack), and control block on the basis of Siemens Program Logic Controller (PLC) which provides fully automated system operation. Switching H2 and steam / water flows is carried out with the help of remotely controlled, pneumatically actuated valves and auxiliary check valves. The H2 discharge line is also equipped with a safety relief valve for H2 venting if overpressure (>210 bar) takes place. Additionally, at P=200 bar the control block switches the system into standby mode when both MH compression modules are cooled down and their gas manifolds are connected to the H2 supply line. The H2 dispensing is independent on the compressor operation and takes from 6 to 15 minutes.

PEM (polymer electrolyte membrane) technology has been used in low-temperature fuel cells and high-temperature fuel cells, as well as water electrolyzers, for many years. Such electrochemical devices are of great interest and importance in the establishment of the so-called Hydrogen Economy . Advancement in polybenzimidazole (PBI)-based high-temperature proton exchange membrane fuel cells (HT-PEMFCs), specifically for stationary applications, has been achieved through systematic optimization of its components. Membrane electrode assembly (MEA) is the heart of an HT-PEMFC, and the fabrication of MEA is a key step for “real” HT-PEMFC applications. A series of studies on developing high-performance MEAs for PBI or ABPBI-based high-temperature fuel cells (120–180°C) are presented in this chapter. Some critical points and perspectives on developing high-performance MEAs are also summarized.

Modeling and simulation studies of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are important in order to better understand the operational behavior of the fuel cell and its performance and lifetime. These models play important roles in the understanding and prediction of HT-PEMFC performance and durability by analyzing various crucial parameters such as species concentrations, local current densities, temperature gradients, and pressure distributions within the fuel cell. These fuel cell modeling studies are often performed at the single cell level or stack level based on specific requirements and it may be either steady-state or dynamic using isothermal or nonisothermal models. The details of the modeling and simulation studies of HT-PEMFC at fuel cell level and stack level models including thermal management and electrochemical models are discussed in this chapter.

Increasing the temperature of polymer electrolyte membrane fuel cells (PEMFCs) implies advantages and disadvantages in terms of material cost, performance, and degradation. Platinum (Pt) is the best catalytic material for high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) electrodes, owing to the possibility it affords of minimizing CO poisoning with temperature enhancement. Nevertheless, it involves an increase in overall cost, mainly due to the larger platinum loadings used (when compared to Pt loadings for low-temperature polymer electrolyte membrane fuel cells). On the other hand, cathodic electrocatalysts still require that the kinetics of the sluggish oxygen reduction reaction be improved. Another disadvantage associated with the use of anodic and cathodic electrocatalysts is the corrosion of both carbon supports and catalytic nanoparticles, which is promoted by the increase in temperature. In this section, the most important factors affecting the performance of these materials are described and a brief description of the state of the art in the design and use of new materials in HT-PEMFCs is presented.

A combined heat and power (CHP) system for energy generation is the most suitable stationary application for fuel cells. High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC)-based fuel cell CHP (FC-CHP) systems, owing to their high operating temperatures, have simpler layouts for auxiliary devices and can operate on reformate with relatively high CO content. The most suitable application of HT-PEMFC technology is in systems where utilization of heat is essential. This makes HT-PEMFC perfect for FC-CHP applications in which electrical energy and heat are produced in a cogenerated manner, enhancing the total efficiency of the overall system. Currently a few HT-PEMFC-based FC-CHP systems are being deployed worldwide and the results of preliminary validation are promising for the technology’s potential commercialization in the near future.

The durability of high temperature proton exchange membrane (HT-PEM) fuel cells is very important for its long term performance and commercialization. Commercialization demands progress, especially in the development of fuel cell catalyst materials and carbon supports. The role of platinum and carbon in the catalytic layer are crucial for the stable performance of a fuel cell. Potential cycling is used to evaluate the stability of platinum and carbon support material of catalyst layer. Fuel cells operated under cycling conditions have lower durability than those operated under steady state conditions. The aim of this work is to study degradation of phosphoric acid doped polybenzimidazole membrane based fuel cell under accelerated potential cycling conditions. Potential cycling degrades fuel cell performance. Understanding this degradation related issues associated with potential cycling is necessary to improve the durability of HT-PEM fuel cell. The fuel cell is cycled between open circuit voltage and 0.5V for 6 minutes per cycle (as represented in figure 1) until 5000 cycles. The performance of fuel cell is characterized using polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry at beginning of life and after the accelerated degradation test to investigate the effect of change in potential step from open circuit voltage to operating voltage of 0.5V. Cathode exhaust is monitored for carbon dioxide using real time infra-red spectroscopy and the condensed water is analyzed for phosphoric acid. Material characterization methods are used to evaluate the degradation mechanisms responsible for the observed performance loss. Figure 1