Ion-conducting membranes are essential components in many electrochemical devices, but they often add substantial cost, limit performance, and are susceptible to degradation. This work investigates membraneless electrochemical flow cells for hydrogen production from water electrolysis that are based on angled mesh flow-through electrodes. These devices can be fabricated with as few as three parts (anode, cathode, and cell body), reflecting their simplicity and potential for low-cost manufacture. 3D printing was used to fabricate prototype electrolyzers that were demonstrated to be electrolyte agnostic, modular, and capable of operating with minimal product crossover. Prototype electrolyzers operating in acidic and alkaline solutions achieved electrolysis efficiencies of 61.9% and 72.5%, respectively, (based on the higher heating value of H 2 ) when operated at 100 mA cm −2 . Product crossover was investigated using in situ electrochemical sensors, in situ imaging, and by gas chromatography (GC). GC analysis found that 2.8% of the H 2 crossed over from the cathode to the anode stream under electrolysis at 100 mA cm −2 and fluid velocity of 26.5 cm s −1 . Additionally, modularity was demonstrated with a three-cell stack, and high-speed video measurements tracking bubble evolution from electrode surfaces provide valuable insight for the further optimization of electrolyzer design and performance. Solar and wind energy have the potential to power the planet without the environmental impact of fossil fuels, but encounter significant challenges to widespread adoption due to their low capacity factors and inherent intermittency.1 In order to overcome this challenge, affordable grid-scale energy storage technology is needed that can make electricity generation from these technologies more widespread.2 One solution to this issue is to convert excess renewable electricity into stored chemical energy in the form of hydrogen gas (H 2 ), 3 which represents a promising candidate for grid scale energy storage and as a carbon-free replacement of fossil fuels in the transportation and industry sectors. 4 Electrolyzers, which use electricity and water to produce hydrogen and oxygen, are well-established commercially available technologies, 5 but the cost of producing H 2 by water electrolysis is currently too expensive.6-8 Presently, much of the cost of producing H 2 by water electrolysis comes from the price of electricity, 6,8 but as the price of electricity from wind and solar continues to decrease and time-of-use pricing schemes become more prevalent, decreasing the cost of electrolyzer technology will be of great importance to making a renewable hydrogen future a reality.The majority of electrolyzers are based on a design in which the cathode and anode are separated by an ion-conducting membrane or diaphragm. 9 The two most common types of electrolyzers are alkaline and polymer electrolyte membrane (PEM) electrolyzers, which are able to electrolyze alkaline and ultra-pure water, respectively. These electrolyzers are mature t...
Carbon-free renewable energy sources, such as solar and wind, have the potential to power the planet without the environmental impact of fossil fuels, but encounter significant challenges due to their intermittency,1 which necessitates significant amounts of energy storage.2 One solution to this issue is the production of hydrogen gas (H2), which has recently emerged as a promising candidate for both clean energy storage as well as a replacement for fossil fuels.3 However, the majority of hydrogen is currently produced by CO2-emitting steam methane reforming.4–6 H2 production from the electrolysis of water offers a promising alternative for producing a storable, carbon-free energy carrier7 and as well as a valuable commodity chemical. This work demonstrates the use of 3D-printed membrane-less electrochemical flow cells for hydrogen production from water splitting with appreciable efficiency and minimal product crossover, as well as the engineering design rules for improvement of the devices. Due to its simplicity and ease of fabrication by additive manufacturing, this novel electrochemical flow cell design has great potential to decrease the cost of H2 production from water spitting. In this design, a flowing electrolyte solution impinges upon two mesh electrodes, which are placed in close proximity at an angle relative to each other to minimize solution resistance (measured to be ~2.3 Ω in 0.25 M H2SO4). The low Ohmic losses enable current densities >100 mA cm-2 in acid using prototype devices with electrodeposited platinum catalysts supported on titanium for both hydrogen and oxygen evolution reactions, with an electrolysis efficiency of 51% at 100 mA cm-2. The product gas streams are separated by a thin divider placed downstream of the electrodes so that there is negligible crossover of H2 or O2 products. The product crossover was monitored using optical and electrochemical sensors, as well as gas chromatography and showed 2.8%.In addition, the devices were able to collect H2 at >90% efficiency. Finally, the scalability of this concept is demonstrated by creating a 3-device stack, each of which was fed via a fluidic manifold to separate the reactant and product streams. This resulted in a linear increase in current with the number of devices present, suggesting that the concept may be scaled to mid- to large-sized production. References (1) Lewis, N. S.; Nocera, D. G. Powering the Planet: Chemical Challenges in Solar Energy Utilization. Proc. Natl. Acad. Sci. USA 2006, 103, 15729–15735. (2) Safaei, H.; Keith, D. W. How Much Bulk Energy Storage Is Needed to Decarbonize Electricity? Energy Environ. Sci. 2015, 10.1039/C5EE01452B. (3) Pellow, M. A.; Emmott, C. J. M.; Barnhart, C. J.; Benson, S. Hydrogen or Batteries for Grid Storage? A Net Energy Analysis. Energy Environ. Sci. 2015, 8, 1938–1952. (4) Navarro, R. M.; Peña, M. A.; Fierro, J. L. G. Hydrogen Production Reactions from Carbon Feedstocks: Fossil Fuels and Biomass. Chem. Rev. 2007, 107, 3952–3991. (5) Kothari, R.; Buddhi, D.; Sawhney, R. L. Comparison of Environmental and Economic Aspects of Various Hydrogen Production Methods. Renew. Sustain. Energy Rev. 2008, 12 (2), 553–563. (6) Abbasi, T.; Abbasi, S. A. “Renewable” Hydrogen: Prospects and Challenges. Renew. Sustain. Energy Rev. 2011, 15 (6), 3034–3040. (7) McKone, J. R.; Lewis, N. S.; Gray, H. B. Will Solar-Driven Water-Splitting Devices See the Light of Day? Chem. Mater. 2014, 26, 407–414.
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