{"id":129,"date":"2020-11-22T15:15:55","date_gmt":"2020-11-22T14:15:55","guid":{"rendered":"http:\/\/jwhaverkort.weblog.tudelft.nl\/?p=129"},"modified":"2022-06-10T10:03:09","modified_gmt":"2022-06-10T08:03:09","slug":"is-there-a-limiting-current-in-alkaline-water-electrolysis","status":"publish","type":"post","link":"https:\/\/jwhaverkort.weblog.tudelft.nl\/?p=129","title":{"rendered":"Is there a limiting current in alkaline water electrolysis?"},"content":{"rendered":"\n<p>Since water is the reactant in water electrolysis, you may be excused for thinking there will be no diffusion limitations. However, at the anode of an alkaline water electrolyzer the reactant is hydroxide (OH-), produced at the cathode. Although usually present at very high concentrations&nbsp;c<sub>0<\/sub>&nbsp;of 6 or 7 M, these ions may deplete at the anode, leading to a limiting current density given by:<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/jwhaverkort.weblog.tudelft.nl\/files\/2020\/11\/i0.png\" alt=\"\" class=\"wp-image-326\" width=\"167\" height=\"73\" \/><\/figure><\/div>\n\n\n\n<p>With a typical separator thickness L of 0.5 mm and effective diffusivity D<sub>&#8211;<\/sub>&nbsp;of&nbsp;&nbsp;10<sup>-9<\/sup> m<sup>2<\/sup>\/s this gives about 0.5 A\/cm<sup>2<\/sup>, in the operating range of modern electrolyzers.<\/p>\n\n\n\n<p>In the following graph, the measured voltage over the separator can be seen to diverge when a current larger than i<sub>0<\/sub> is applied. The dashed lines show the behavior expected from a simple model.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/jwhaverkort.weblog.tudelft.nl\/files\/2020\/11\/phitot-300x215.png\" alt=\"\" class=\"wp-image-327\" width=\"435\" height=\"308\" \/><\/figure><\/div>\n\n\n\n<p>For more information on the these measurements, the model, and their relevance for hydrogen production see:<\/p>\n\n\n\n<p><a href=\"https:\/\/doi.org\/10.1016\/j.powera.2020.100034\">Haverkort, J. W., &amp; Rajaei, H. (2020). Electro-osmotic flow and the limiting current in alkaline water electrolysis.&nbsp;<i>Journal of Power Sources Advances<\/i>,&nbsp;<i>6<\/i>, 100034.0034<\/a><\/p>\n\n\n\n<p>and<\/p>\n\n\n\n<p><a href=\"https:\/\/doi.org\/10.1103\/PhysRevApplied.14.044047\">Haverkort, J. W. (2020). Modeling and Experiments of Binary Electrolytes in the Presence of Diffusion, Migration, and Electro-Osmotic Flow.&nbsp;<i>Physical Review Applied<\/i>,&nbsp;<i>14<\/i>(4), 044047<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Since water is the reactant in water electrolysis, you may be excused for thinking there will be no diffusion limitations. However, at the anode of an alkaline water electrolyzer the reactant is hydroxide (OH-), produced at the cathode. Although usually &hellip; <a href=\"https:\/\/jwhaverkort.weblog.tudelft.nl\/?p=129\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":6225,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,4,6,1],"tags":[],"_links":{"self":[{"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/posts\/129"}],"collection":[{"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/users\/6225"}],"replies":[{"embeddable":true,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=129"}],"version-history":[{"count":7,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/posts\/129\/revisions"}],"predecessor-version":[{"id":329,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=\/wp\/v2\/posts\/129\/revisions\/329"}],"wp:attachment":[{"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=129"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jwhaverkort.weblog.tudelft.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}