Volume 1, Issue 4, Pages 651-658 (December 2017) Membraneless Electrolyzers for Low-Cost Hydrogen Production in a Renewable Energy Future  Daniel V. Esposito  Joule  Volume 1, Issue 4, Pages 651-658 (December 2017) DOI: 10.1016/j.joule.2017.07.003 Copyright © 2017 Elsevier Inc. Terms and Conditions

Joule 2017 1, 651-658DOI: (10.1016/j.joule.2017.07.003) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Economics of Water Electrolysis (A) Electricity operating costs (opex) as a function of electrolyzer efficiency and the price of electricity. (B) Capital expenditures (capex) of an electrolyzer system normalized to the total amount of H2 generated over a 10 year lifetime while operating at 1.5 A cm−2 and an electrolysis efficiency of 78%. The horizontal dashed lines in both plots correspond to the levelized cost of producing H2 by SMR, based on a study by the US Department of Energy4 and the average 2016 industrial price of natural gas in the US (see Supplemental Information). The average price of electricity to industrial customers in the US is for March 2017 and obtained from the US Energy Information Administration's Electric Power Monthly Report available at www.eia.gov. Electrolyzer efficiency is based on the higher heating value (HHV) of H2. Joule 2017 1, 651-658DOI: (10.1016/j.joule.2017.07.003) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Simplified Side-View Schematics of Low-Temperature Electrolyzer Technologies (A–D) Conventional (A) PEM and (B) alkaline electrolyzer cells. Emerging membraneless electrolyzers based on (C) flow-by electrodes and (D) flow-through electrodes. The inset in (D) shows a 3D view of a mesh flow-through electrode evolving O2 as electrolyte passes through holes in the mesh. Joule 2017 1, 651-658DOI: (10.1016/j.joule.2017.07.003) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Ohmic Losses and the Relation of Operating Current Density to Allowable Capital Costs of an Electrolyzer (A) Calculated ohmic voltage drop (V = IRs) for electrolysis at 0.5 A cm−2 as a function of the electrolyte conductivity and distance between the anode and cathode, which are assumed to be parallel to each other and separated only by electrolyte. (B) Tie lines showing the combinations of current density and area-normalized electrolyzer capital cost (CCA) that are necessary to achieve an H2 production cost of 1.59 $ kg−1 with a CF of 20%. Curves are based on a simple techno-economic model described in the Supplemental Information. In all curves, it is assumed that electrolyzers have a 10 year lifetime, and a constant efficiency of 75% based on the HHV of H2. Joule 2017 1, 651-658DOI: (10.1016/j.joule.2017.07.003) Copyright © 2017 Elsevier Inc. Terms and Conditions