This work demonstrated a robust, scalable cell architecture for electroreduction of CO2 (CO2R). An up to 90% faradaic efficiency for the conversion of CO2R to formate at 500 mA/cm2 was realized at a 25 cm2 gas diffusion electrode (GDE) with a carbon-supported SnO2 electrocatalyst. A 1.27 mm thick catholyte was used between the bipolar membrane and cathode GDE, which could be further reduced to tens of micrometers upon refinement. The deconvolution of the potential drop from each individual component/process guides the pathways to higher energy efficiencies of CO2R at this platform. Significant changes in the agglomerate size and aspect ratio on the electrode before and after an 11 h test were revealed by nano-CT, suggesting reduced CO2 accessibility from electrode degradation. The versatility of this CO2R testing platform enables the ability to assess materials, components, and interactions at scales more in line with future devices.
Bipolar membranes (BPMs) are the enabling component of many promising electrochemical devices used for separation and energy conversion. Here, we describe the development of high-performance BPMs, including two-dimensional BPMs (2D BPMs) prepared by hot-pressing two preformed membranes and three-dimensional BPMs (3D BPMs) prepared by electrospinning ionomer solutions and polyethylene oxide. Graphene oxide (GO x ) was introduced into the BPM junction as a water-dissociation catalyst. We assessed electrochemical performance of the prepared BPMs by voltage–current (V–I) curves and galvanostatic electrochemical impedance spectroscopy. We found the optimal GO x loading in 2D BPMs to be 100 μg cm–2, which led to complete coverage of GO x at the interface. The integration of GO x beyond this loading moderately improved electrochemical performance but significantly compromised mechanical strength. GO x -catalyzed 2D BPMs showed comparable performance with a commercially available Fumasep BPM at current densities up to 500 mA cm–2. The 3D BPMs exhibited even better performance: lower resistance and higher efficiency for water dissociation and substantially higher stability under repeated cycling up to high current densities. The improved electrochemical performance and mechanical stability of the 3D BPMs make them suitable for incorporation into CO2 electrolysis devices where high current densities are necessary.
Photoelectrochemical (PEC) water splitting is an elegant method of converting sunlight and water into H fuel. To be commercially advantageous, PEC devices must become cheaper, more efficient, and much more durable. This work examines low-cost polycrystalline chalcopyrite films, which are successful as photovoltaic absorbers, for application as PEC absorbers. In particular, Cu-Ga-Se films with wide band gaps can be employed as top cell photocathodes in tandem devices as a realistic route to high efficiencies. In this report, we demonstrate that decreasing Cu/Ga composition from 0.66 to 0.31 in Cu-Ga-Se films increased the band gap from 1.67 to 1.86 eV and decreased saturated photocurrent density from 18 to 8 mA/cm as measured by chopped-light current-voltage (CLIV) measurements in a 0.5 M sulfuric acid electrolyte. Buffer and catalyst surface treatments were not applied to the Cu-Ga-Se films, and they exhibited promising stability, evidenced by unchanged CLIV after 9 months of storage in air. Finally, films with Cu/Ga = 0.36 (approximately stoichiometric CuGaSe) and 1.86 eV band gaps had exceptional durability and continuously split water for 17 days (∼12 mA/cm at -1 V vs RHE). This is equivalent to ∼17 200 C/cm, which is a world record for any polycrystalline PEC absorber. These results indicate that CuGaSe films are prime candidates for cheaply achieving efficient and durable PEC water splitting.
Fuel cells are considered to be one of the most the most promising energy conversion devices for both residential and transportation applications due to their high electrical efficiencies, low operating temperatures, and zero tailpipe emissions.1-2 Significant advancements have been made in the development of ORR electrocatalysts to enable attainment of the DOE target of 440 mA/mgPt at 0.9V and 150 kPa. Specifically, utilizing nanostructured carbon materials with internal porosity resulted in increased platinum dispersion, higher electrochemically available surface areas, and higher mass acitivites.3 Additionally, transition metal Pt alloys, specifically, Ni and Co, have shown to increase the activity per Pt site, enabling improvements in mass acitivity.4 However, when these different sets of Pt or PtM/Carbon materials are incorporated into dispersed PEMFC electrodes the time, potential and environmental parameters, also known as “break-in” or “conditioning”, required to achieve optimum performance can be vastly different. While several publications have presented baseline electrocatalyst performance values,5-7 and/or demonstrated different methods for fabricating electrodes and standardizing MEA performance,8-9 the impact of MEA conditioning on performance has rarely been discussed in detail. The absence of a detailed discussion of lab-scale MEA fabrication methods in conjunction with conditioning can lead to the reporting of erroneous experimental observations related to purported improvements in electrocatalytic activity or device design. Previous studies by Neyerlin et. al.10 have demonstrated the importance of MEA conditioning on observed mass activity and high current density performance alike. In this study, we expand upon our previous findings, examining the influence of conditioning on 4 different commercially available catalysts: (i) 50wt.% Pt/Vulcan (TKK), (ii) 50 wt% Pt/HSC (TKK), (iii) 30 wt.% PtCo (Umicore) and (iv) 30 wt.% Pt/HSC (Umicore) at three different loadings (0.05, 0.1 and 0.15 mgPt cm-2). The objective was to investigate and measure the effects of various break-in processes on oxygen reduction reaction (ORR) mass and specific activity (MA, SA), electrochemical surface area (ECA) and H2-Air polarization curves to formulate a fair and comparative assessment of all the state-of-the-art electrocatalysts investigated in this study. Preliminary results have shown that the conditioning procedures might need to be re-considered based on the particular catalyst and catalyst layer loading in order to obtain peak performances. The results from this study will not only provide possible pathways towards improving the performance of low loaded high activity catalysts that is needed to meet DOE targets for fuel cell commercialization, but also demonstrate the importance of implementing systematic protocols for increased catalyst utilization. References M. K Debe, Nature, 2012, 486, 43−51. Handbook of Fuel Cells: Advances in Electrocatalyst, Materials, Diagnostics, and Durability; Vielstich, W., Yokokawa, H., Gasteiger, H.A., Eds.; John Wiley & Sons: Hoboken, NJ, 2009. S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature, 2001, 412(6843), 169-172. D. Wang, H. L. Xin, R. Hovden, H. Wang, Y. Yu, A. Muller, F. J. DiSalvo, H. D. Abruña, Nature materials, 2013, 12(1), 81-87. H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B: Env., 2005, 56, 9. H. A. Gasteiger, J. E. Panels, and S. G. Yan, J. Power Sources, 2004, 127, 162. Y. Garsany, O. A. Baturina, K. E. Swider-Lyons, S. S. Kocha, Anal. Chem., 2010, 82 (15), 6321-6328. M. B. Sassin, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, Anal. Chem., 2017, 89 (1), 511–518 V. Yarlagadda, S. E. McKinney, C. L. Keary, L. Thompson, B. Zulevi, and A. Kongkanand, J. Electrochem. Soc., 2017, 164(7), F845-F849. K. C. Neyerlin, 232nd ECS Meeting, National Harbor, MD Oct. 1-5, 2017.
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