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.

The cost and performance of proton exchange membrane fuel cells strongly depend on the cathode electrode due to usage of expensive platinum (Pt) group metal catalyst and sluggish reaction kinetics. Development of low Pt content high performance cathodes requires comprehensive understanding of the electrode microstructure. In this study, a new approach is presented to characterize the detailed cathode electrode microstructure from nm to μm length scales by combining information from different experimental techniques. In this context, nanoscale X-ray computed tomography (nano-CT) is performed to extract the secondary pore space of the electrode. Transmission electron microscopy (TEM) is employed to determine primary C particle and Pt particle size distributions. X-ray scattering, with its ability to provide size distributions of orders of magnitude more particles than TEM, is used to confirm the TEMdetermined size distributions. The number of primary pores that cannot be resolved by nano-CT is approximated using mercury intrusion porosimetry. An algorithm is developed to incorporate all these experimental data in one geometric representation. Upon validation of pore size distribution against gas adsorption and mercury intrusion porosimetry data, reconstructed

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This two-part study characterizes the structural and transport properties of polymer electrolyte fuel cell (PEFC) cathode catalyst electrode. The agglomerates comprising the electrode are characterized with nano scale resolution X-ray computed tomography (nano-CT). A hybrid reconstruction technique is used to further refine the 3-D agglomerate microstructure and obtain 1-nm voxel resolution of the constituent catalyst, ionomer, carbon support and primary and secondary pore phases. Our analysis of nano-CT data shows that the electrode composition is heterogeneous and the agglomerates have structural heterogeneities in terms of size and composition. There is a strong correlation between the ionomer to carbon weight ratio (I/C) and agglomerate microstructure, suggesting that ionomer plays role in formation of larger agglomerates. With the hybrid reconstructions, we show that ionomer film thickness is spatially non-uniform inside the agglomerate and is strongly dependent on the I/C. Smaller agglomerate size and high I/C are shown to favor the ionomer impregnation. We demonstrate that the majority of the primary pores are smaller than 15 nm for I/C = 0.8 and higher I/C reduces the primary pore size. We also characterize the uniformity of the catalyst distribution and show that the majority of the catalyst is located away from the agglomerate surface.

The complex porous structure of the PEM fuel cell catalyst layer (CL) necessitates the use of multiscale modeling strategies such as the agglomerate approach. In this study a 2D steady-state model for the cathode CL is developed using the spherical agglomerate approach. A new, more accurate, method is introduced to determine the effective agglomerate surface area, which plays a key role in estimating diffusion losses in the CL. Specifically, the reduction in the effective surface area due to overlapping particles is modeled geometrically based on a sphere-packing approach. In addition, the equations for the agglomerate model are reformulated to correctly account for the agglomerate surface area reduction due to overlapping particles. The importance of an accurate geometric model for the effective surface area is demonstrated by investigating the effect of CL composition on performance, and the results show that the new method provides more realistic predictions than the existing approach. Results from the new approach for optimal Pt loading, ionomer loading, and Pt|C ratio show good agreement with experimental results. Great strides have been made in proton exchange membrane (PEM) fuel cell research since the introduction of the technology in the early 1960s. Computational models represent a major tool for the design and development of PEM fuel cells because they decrease the dependence on expensive and time-consuming experimental procedures. Accurate computational models can also provide key insights into the fundamental processes that govern fuel cell performance. The overall accuracy of computational models depends strongly on the description of the catalyst layer (CL) as all the critical electrochemical reactions, and heat and mass transport processes occur within the CL. Therefore, developing better modeling strategies for the CL has been an important research objective to obtain a realistic representation of PEM fuel cell behavior.Catalyst layer modeling approaches, which have grown in complexity in the past decades, were described in detail in. 1 Here, we present only a brief review. Among the models reported, the interface model 2-4 is the simplest approach as it represents all of the CL activity as boundary conditions applied at the interface between the membrane and the gas diffusion layer (GDL). The macro-homogenous model [4][5][6][7] is a more advanced approach that utilizes the effective medium theory and approximates the CL as a porous matrix of gas pores, platinum, carbon, and electrolyte. The most comprehensive device-level model to date is the agglomerate approach [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] as it represents CL activity as a multiscale problem. Overall, the CL is assumed to consist of gas pores and aggregates of C|Pt particles that are covered by an electrolyte film. The agglomerate approach attempts to model the C|Pt aggregates (shown schematically in Fig. 1a) that are typically seen in microscopic images of the CL. For simplicity, the aggregate microstructure, de...