Skip to main content

Oxygen vs Air in PEM Fuel Cells

Most of the time, the designer doesn't have the choice between air and oxygen when assembling a PEM fuel cell. Oxygen is employed in systems that don't depend on air to operate, such as submarine and spacecraft (when that is not the case, air is used). However, the performance of a PEM fuel cell is greatly improved when oxygen is used. That happens because of three factors:
  • The increase in partial pressure of oxygen makes the 'no loss' open circuit voltage rise, as appointed by the Equation of Nernst (https://en.wikipedia.org/wiki/Nernst_equation).
  • Use of better catalyst sites reduces the activation over-voltage.
  • The mass transport or concentration over-voltage losses are reduced by the increase in the limiting current, which is an event caused by the absence of nitrogen(a gas that contributes for this kind of loss at high current densities.
Some results have showed that the change from air to oxygen in a PEMFC can increase performance by as much as 30%. 

Reference:

LARMINIE, James; DICKS, Andrew. Fuel Cell Systems Explained. 2. ed. West Sussex, England: Wiley & Sons Ltd., 2003. 418 p.


Comments

Popular posts from this blog

Photovoltaics: Band Diagram

In the previous post we discussed silicon, which is the most used material in photovoltaics. In this post, we introduce the band diagram, for which we will use silicon as an example. We will start our discussion of the band diagram with the Bohr model of the silicon atom. In semiconductor materials the outer shell of the atom, which is called the valence shell, is not completely filled. The outer shell of silicon contains 4 out of the possible 8 electrons, which we call valence electrons. As we discussed in the previous post, each silicon atom in a crystalline structure is bonded to four other silicon atoms. The bonds between the silicon atoms are called covalent bonds. These bonds actually consist of two valence electrons that are shared by two silicon atoms. All valence electrons are fixed in the lattice, forming covalent bonds, and are therefore immobile. However, at a temperature above absolute zero, thermal energy is supplied to these miconductor and some of the vale...

Watching videos on the Internet also harms the environment

Surprisingly, even the videos we watch on the Internet have an impact on the environment. A new report indicates that the internet is one of the top "villains" in the digital sector's carbon footprint, which now accounts for 4% of global greenhouse gas emissions. This share could double by 2025, leaving the digital sector on a par with road transport, as energy consumption in this sector is increasing at the rate of 9% per year. Published by the French research website The Shift Project, the report "Climate Crisis: The Unsustainable Use of Online Video" quantifies the impact of Internet video (VoD, "tubes", pornography, social networks and others) on the environment and the global climate. The study shows that, within all Internet data, online videos account for about 60 percent of the stream, or the largest volume of greenhouse gas emissions in the industry, with about 300 megatonnes of carbon dioxide equivalent (tCO2e). Of this total emission,...

Photovoltaics: Silicon

Welcome to this new post about semiconductor physics. Before we delve into all the important topics of semiconductor physics that are relevant to solar cells, we need to talk about silicon. Silicon is one of the most important materials when it comes to solar cells and we will be using it throughout this post series as an example for all the semiconductor concepts we will be going into. This will only be a short introduction to silicon, and there will be an extensive post series on silicon-based solar cells in the following course, Photovoltaic Technologies. Let’s start our discussion by looking at the reasons why silicon is the most used material for fabricating solar cells. The first successful silicon solar cell was fabricated in the Bell Laboratories in US in 1954. At present, the photovoltaic industry is dominated by silicon-based solar cells with 90%share of the market. Silicon is the most widespread material used for solar cells. But why is it that silicon is used so much?...