Modeling and control design of a Vienna rectifier based electrolyzer

Hydrogen production is an interesting alternative of storing energy. Electrolyzers produce hydrogen through water electrolysis; the resulting hydrogen is later used to generate electricity by using fuel cells, that reverse the process. Electrolyzers use rectifiers to convert the grid ac voltage into dc voltage for supplying the electrolyzer cells. Previous research used a rectification process based on conventional rectifiers (diode-or thyristor-based) which draw non-sinusoidal current from the main grid. This requires increased filtering to prevent power quality problems and equipment malfunctioning/failure. In addition, previous literature assumed simplified models for the power electronics converters and lacked a detailed control system. The Vienna rectifier is a non-regenerative converter that produces sinusoidal currents with low losses due to the reduced number of active switches. This manuscript proposes using the Vienna rectifier as an interface to connect electrolyzers to the ac grid. The dc voltage applied to the electrolyzer is regulated by using another DC-DC converter, which is selected to be a synchronous buck converter for simplicity and maximum efficiency. In this paper, the models of the Vienna rectifier, synchronous buck converter, and the electrolyzer are developed along with their respective controls. The control system has the ability to function in two operation modes for the overall reference: hydrogen production and power demand. The first one is adequate for grid-connected operation and the later for off-grid operation. Simulation results are given to show the validity of the proposed procedures

Natural gas fuel and greenhouse gas emissions in trucks and ships

Natural gas is a transport fuel which may help reduce greenhouse gas emissions in shipping and trucks. However, there is some disagreement regarding the potential for natural gas to provide significant improvements relative to current ships and trucks. In 2015, road freight represented ~7% of global energy related CO2 emissions, with international shipping representing ~2.6% of global emissions. These emissions are also expected to grow, with some estimates suggesting road freight emission growing by a third, and shipping emissions growing by between 50% and 250% from 2012 to 2050, making absolute emissions reductions challenging. In addition, reducing emissions in ships and trucks has proved technically difficult given the relatively long distances that ships and trucks travel. This paper documents a systematic review of literature detailing well-to-wheel/wake greenhouse gas emissions and economic costs in moving from diesel and heavy fuel oil to natural gas as a fuel for trucks and ships. The review found a number of important issues for greenhouse gas reduction. First, moderate greenhouse gas reductions of 10% were found when switching to natural gas from heavy fuel oil in shipping when comparing the lowest estimates. Comparing lowest well-to-wheel greenhouse gas emissions estimates for trucks, the benefit of switching to natural gas fuel is approximately a 16% reduction in greenhouse gas emissions. However, these emissions are highly variable, driven particularly by methane emissions in exhaust gas. Given this, in the worst cases natural gas ships and trucks emit more greenhouse gasses than the diesel trucks and heavy fuel oil ships that they would replace. It appears relatively cost effective to switch to natural gas as a transport fuel in ships and trucks. However, the limited emissions reduction potential raises questions for the ongoing role of natural gas to reduce greenhouse gas emissions in line with the challenging greenhouse gas reduction targets emerging in the transport sector

Life beyond 30: Probing the-20 < M (UV) <-17 Luminosity Function at 8 < z < 13 with the NIRCam Parallel Field of the MIRI Deep Survey

We present the ultraviolet luminosity function and an estimate of the cosmic star formation rate density at 8 8 galaxy candidates based on their dropout nature in the F115W and/or F150W filters, a high probability for their photometric redshifts, estimated with three different codes, being at z > 8, good fits based on χ 2 calculations, and predominant solutions compared to z < 8 alternatives. We find mild evolution in the luminosity function from z ∼ 13 to z ∼ 8, i.e., only a small increase in the average number density of ∼0.2 dex, while the faint-end slope and absolute magnitude of the knee remain approximately constant, with values α = − 2.2 ± 0.1, and M * = − 20.8 ± 0.2 mag. Comparing our results with the predictions of state-of-the-art galaxy evolution models, we find two main results: (1) a slower increase with time in the cosmic star formation rate density compared to a steeper rise predicted by models; (2) nearly a factor of 10 higher star formation activity concentrated in scales around 2 kpc in galaxies with stellar masses ∼108 M ⊙ during the first 350 Myr of the universe, z ∼ 12, with models matching better the luminosity density observational estimations ∼150 Myr later, by z ∼ 9

Energy demand and greenhouse gas emissions from urban passenger transportation versus availability of renewable energy in the Canadian Lower Fraser Valley

NRC publication: Ye

Reference Electrodes for Failure Diagnostics in Fuel Cells

NRC publication: Ye

A Vaporization-Exchange Model for Water Sorption and Flux in Nafion

model is developed to describe sorption or desorption of water from planar Nafion membranes with one face contacting stagnant water or saturated water vapor and the opposite face exposed to flowing gas. Interfacial evaporation/condensation kinetics is considered along with bulk water transport. Simplifying assumptions yield analytical formulas that relate the steady-state or transient system response to the gas flow rate. The approximate predictions correlate well with experimental data gathered under various conditions. Water transport rates are found to be limited by interfacial vaporization-exchange kinetics, rather than bulk percolation or diffusion, when membrane slabs are thinner than approximately 300 \uce\ubcm.NRC publication: Ye

Microscale X-ray tomographic investigation of the interfacial morphology between the CL and MPL in PEMFCs

The interfacial morphology between the catalyst layer (CL) and micro porous layer (MPL) influences the properties and performance of proton exchange membrane fuel cells (PEMFCs). Here we report a direct method to investigate the CL-MPL interfacial morphology of stacked and compressed gas diffusion layer (GDL with MPL)-catalyst coated membrane (CCM) assemblies. The area, origin and dimensions of interfacial gaps are studied with high-resolution X-ray micro computed tomography (X-μCT). The interfacial gap area (fraction of the CL-MPL interface separated by gaps) is higher for GDL-CCM assemblies with large differences in the surface roughness between the CL and MPL but reduces with increasing compression and with increased similarity in roughness. Relatively large continuous gaps are found in proximity to cracks in the MPL. These are hypothesized to form due to the presence of large pores on the surface of the GDL. Relatively small gaps are induced by the surface roughness features throughout the CL-MPL interface. From the results, smaller pores on the GDL surface serving as substrate for the MPL could reduce the number of MPL crack-induced gaps. Moreover, adjusting the CL and MPL surface roughness parameters to achieve similar orders of roughness can improve the surface mating characteristics of these two critical fuel cell components.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult

A review of accelerated stress tests of MEA durability in PEM fuel cells

This paper is a review of recent work done on accelerated stress tests in the study of PEM fuel cell durability, with a primary focus on the main components of the membrane electrode assembly (MEA). The accelerated stressors for each component under different conditions are outlined, in an attempt to gain a detailed understanding of cell degradation with respect to microstructural change and performance attenuation in the perfluorosulfonic acid membrane, catalyst, and gas diffusion layers. Various techniques for evaluating the components' performance are presented, along with representative mitigation strategies. In addition, different degradation mechanisms proposed in recent publications are briefly reviewed.Peer reviewed: YesNRC publication: Ye