{"id":4681,"date":"2014-10-07T20:56:35","date_gmt":"2014-10-07T19:56:35","guid":{"rendered":"http:\/\/www.theoillamp.co.uk\/?p=4681"},"modified":"2014-10-09T15:46:56","modified_gmt":"2014-10-09T14:46:56","slug":"hydrogen-economy-myth","status":"publish","type":"post","link":"https:\/\/www.theoillamp.co.uk\/?p=4681","title":{"rendered":"The hydrogen economy myth-part 1"},"content":{"rendered":"

\"Fuel_Cell_Apparatus-_Pressurized_Liquid_Reactants\"<\/a>Been having a bit of a blether about the hydrogen economy recently after a supposed breakthrough in hydrogen production at Glasgow University.\u00a0 This got me thinking about this whole hydrogen economy myth which we covered in our book<\/a>.\u00a0 I’m afraid these two posts are going to be complicated so if you don’t like science leave now…<\/p>\n

For the purposes of these posts we will mainly be talking about fuel cells and more specifically proton exchange membrane fuel cells (PEMFC’s).\u00a0 These have a platinum anode and cathode separated by a semi-permeable membrane (usually TEFLON with sulphonate groups added).\u00a0 The platinum acts as a catalyst.\u00a0 To make hydrogen we use an electrolyser.\u00a0 In this the platinum anode and cathode are in the same compartment.<\/p>\n

At the anode the reaction (technically an oxidation reaction) is;<\/p>\n

2 H2<\/sub>O(l<\/a><\/i>) \u2192 O2<\/sub>(g<\/i>) + 4 H+<\/sup>(aq<\/i>) + 4e\u2212<\/sup><\/p>\n

At the cathode (technically a reduction reaction) is ;<\/p>\n

2 H+<\/sup>(aq<\/a><\/i>) + 2e\u2212<\/sup> \u2192 H2<\/sub>(g<\/a><\/i>)<\/p>\n

combining these two and balancing gives;<\/p>\n

2 H2<\/sub>O(l<\/i>) \u2192 2 H2<\/sub>(g<\/i>) + O2<\/sub>(g<\/i>)<\/p>\n

In the fuel cell all the above are reversed.\u00a0 At the anode hydrogen is split by the catalyst to protons and electrons.\u00a0 The electrons flow through the conductor joining the two and some are used by us to do “useful work”.\u00a0 At the cathode oxygen, electrons from the circuit and protons which have migrated though the semi-permeable membrane combine to make water.\u00a0 The idea is that the semi-permeable membrane allows the protons to migrate to the cathode compartment where it combines with the hydrogen and oxygen in the reverse reaction but does not allow the oxygen to enter the anode compartment.<\/p>\n

All chemical reactions have three criteria that are vital.\u00a0 The first is kinetics<\/em>, that is the speed<\/em> of the reaction.\u00a0\u00a0 The second is the thermodynamics of the reaction.\u00a0 This is whether the reaction is energetically<\/em> favourable.\u00a0 Very importantly thermodynamics also has a bearing on the maximum efficiency of any chemical reactions and how much energy can be produced.\u00a0 The third is where the chemical equilibrium lies i.e. whether the reaction intrinsically favours formation of the products or the reverse.\u00a0 Both the forward and reverse reactions above require a catalyst.\u00a0 This speeds up the reaction (kinetics), but has no bearing on the thermodynamics of whether the reaction is favourable.\u00a0 Most reactions are reversible.\u00a0 As reactants proceed to products if the products are not removed the reverse reaction will occur more and more until potentially an equilibrium is reached with no overall change.\u00a0 Equilibrium however can<\/em> be related to thermodynamics.<\/p>\n

Splitting water to hydrogen is not<\/em> energetically<\/em> favourable and spontaneous change will not occur, therefore energy in the form of electrons has to be provided.\u00a0 The reverse reaction is<\/em> energetically<\/em> favourable and it produces energy in the form of electrons.<\/p>\n

To finish part 1 of this post, thermodynamics has two laws (actually three but the third is irrelevant here) and three components (enthalpy<\/strong> (H), entropy<\/strong> (S) and free energy<\/strong> (G).<\/p>\n

The first<\/strong> law says that energy can neither be created or destroyed.\u00a0 This has a number of\u00a0 connotations but one is that it does not matter how you get from reactant to product H, S and G are the same by whichever route you go.<\/p>\n

The second<\/strong> states that no spontaneous change occurs unless the entropy in a system increases.<\/p>\n

The three components are heat (self-explanatory often reactions produce or require heat).\u00a0 Entropy or disorder is slightly harder to visualise.\u00a0 The greater the disorder the greater the entropy.\u00a0 If you have gas in a cylinder its entropy is low, open a valve and its entropy increases to the maximum extent possible as gas molecules exit chaotically\u00a0 filling the space.\u00a0 Free energy is the amount of energy available to do “useful work”, in our example above the electrons liberated as hydrogen is split into protons and electrons.<\/p>\n

The three are related by the following equation;<\/p>\n

\u0394G=\u0394H-T\u0394S<\/p>\n

\u0394 means sum of the change over the reaction between the start and finish and where T is the temperature (usually taken as 25\u00baC) at which a reaction occurs.\u00a0 For spontaneous change to take place \u0394G must be negative.\u00a0 So in our example above;<\/p>\n

H2<\/sub> + O2<\/sub> -> H2<\/sub>O<\/p>\n

must have a negative value of \u0394G.\u00a0 The more the equilibrium moves towards the products the more negative \u0394G will be (up to a theoretical maximum).\u00a0 (I won’t bore you with the equation linking chemical equilibrium and thermodynamics.)\u00a0\u00a0Equilibrium cannot ultimately trump thermodynamics in making a reaction occur, but can influence it.<\/strong>\u00a0 Reaction conditions can be tweaked to maximise all the above, using other compounds to “donate” free energy or heat or pressure.\u00a0 In part 2 of the hydrogen economy myth I will look at maximum and practical efficiencies and why in my view the hydrogen economy doesn’t add up.<\/p>\n

Neil<\/p>\n

clipart from openclipart.org<\/p>\n","protected":false},"excerpt":{"rendered":"

Been having a bit of a blether about the hydrogen economy recently after a supposed breakthrough in hydrogen production at Glasgow University.\u00a0 This got me thinking about this whole hydrogen economy myth which we covered in our book.\u00a0 I’m afraid … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[28,4,1],"tags":[43],"class_list":["post-4681","post","type-post","status-publish","format-standard","hentry","category-other","category-renewables","category-uncategorized","tag-hydrogen-economy"],"yoast_head":"\nhydrogen economy<\/title>\n<meta name=\"description\" content=\"Been having a bit of a blether about the hydrogen economy recently after a supposed breakthrough in hydrogen production at Glasgow University.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.theoillamp.co.uk\/?p=4681\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"admin\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681\",\"url\":\"https:\/\/www.theoillamp.co.uk\/?p=4681\",\"name\":\"hydrogen economy\",\"isPartOf\":{\"@id\":\"https:\/\/www.theoillamp.co.uk\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681#primaryimage\"},\"image\":{\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681#primaryimage\"},\"thumbnailUrl\":\"http:\/\/www.theoillamp.co.uk\/wp-content\/uploads\/2014\/10\/Fuel_Cell_Apparatus-_Pressurized_Liquid_Reactants-300x171.png\",\"datePublished\":\"2014-10-07T19:56:35+00:00\",\"dateModified\":\"2014-10-09T14:46:56+00:00\",\"author\":{\"@id\":\"https:\/\/www.theoillamp.co.uk\/#\/schema\/person\/b6f2831189b0d01294e9672bb540ba6f\"},\"description\":\"Been having a bit of a blether about the hydrogen economy recently after a supposed breakthrough in hydrogen production at Glasgow University.\",\"breadcrumb\":{\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.theoillamp.co.uk\/?p=4681\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681#primaryimage\",\"url\":\"http:\/\/www.theoillamp.co.uk\/wp-content\/uploads\/2014\/10\/Fuel_Cell_Apparatus-_Pressurized_Liquid_Reactants-300x171.png\",\"contentUrl\":\"http:\/\/www.theoillamp.co.uk\/wp-content\/uploads\/2014\/10\/Fuel_Cell_Apparatus-_Pressurized_Liquid_Reactants-300x171.png\"},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.theoillamp.co.uk\/?p=4681#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.theoillamp.co.uk\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"The hydrogen economy myth-part 1\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.theoillamp.co.uk\/#website\",\"url\":\"https:\/\/www.theoillamp.co.uk\/\",\"name\":\"The oil lamp - 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