Scalable Hydrogen Production with a 3D-Printed Membraneless Water Electrolyzer

Abstract

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.