Understanding Limitations in Electrochemical Conversion to CO at Low CO2 Concentrations.

Low-temperature electrochemical CO2 reduction has demonstrated high selectivity for CO when devices are operated with pure CO2 streams. However, there is currently a dearth of knowledge for systems operating below 30% CO2, a regime interesting for coupling electrochemical devices with CO2 point sources. Here we examine the influence of ionomer chemistry and cell operating conditions on the CO selectivity at low CO2 concentrations. Utilizing advanced electrochemical diagnostics, values for cathode catalyst layer ionic resistance and electrocatalyst capacitance as a function of relative humidity (RH) were extracted and correlated with selectivity and catalyst utilization. Staying above 20% CO2 concentration with at least a 50% cathode RH resulted in >95% CO/H2 selectivity regardless of the ionomer chemistry. At 10% CO2, however, >95% CO/H2 selectivity was only obtained at 95% RH under scenarios where the resulting electrode morphology enabled high catalyst utilization.

Elucidation of Critical Catalyst Layer Phenomena toward High Production Rates for the Electrochemical Conversion of CO to Ethylene.

This work utilizes EIS to elucidate the impact of catalyst-ionomer interactions and cathode hydroxide ion transport resistance (RCL,OH-) on cell voltage and product selectivity for the electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for RCL,OH- and ca. a 25% change in electrode porosity. Decreasing RCL,OH- results in improved ethylene Faradaic efficiency (FE), up to ∼57%, decrease in hydrogen FE, by ∼36%, and reduction in cell voltage by up to 1 V at 700 mA/cm2. Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for non-hydrogen products in a 25 cm2 membrane electrode assembly at 700 mA/cm2 and <3 V. Additionally, the implications of optimizing RCL,OH- is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process.

A scalable membrane electrode assembly architecture for efficient electrochemical conversion of CO2 to formic acid.

The electrochemical reduction of carbon dioxide to formic acid is a promising pathway to improve CO2 utilization and has potential applications as a hydrogen storage medium. In this work, a zero-gap membrane electrode assembly architecture is developed for the direct electrochemical synthesis of formic acid from carbon dioxide. The key technological advancement is a perforated cation exchange membrane, which, when utilized in a forward bias bipolar membrane configuration, allows formic acid generated at the membrane interface to exit through the anode flow field at concentrations up to 0.25 M. Having no additional interlayer components between the anode and cathode this concept is positioned to leverage currently available materials and stack designs ubiquitous in fuel cell and H2 electrolysis, enabling a more rapid transition to scale and commercialization. The perforated cation exchange membrane configuration can achieve >75% Faradaic efficiency to formic acid at <2 V and 300 mA/cm2 in a 25 cm2 cell. More critically, a 55-hour stability test at 200 mA/cm2 shows stable Faradaic efficiency and cell voltage. Technoeconomic analysis is utilized to illustrate a path towards achieving cost parity with current formic acid production methods.

Measurement of Contact Angles at Carbon Fiber-Water-Air Triple-Phase Boundaries Inside Gas Diffusion Layers Using X-ray Computed Tomography.

Gas diffusion layers (GDLs) are porous carbonaceous layers that are widely used in energy conversion and storage devices. Simulation of water transport through GDLs, in a polymer electrolyte fuel cell (PEFC), for example, typically uses goniometer-measured external contact angles. Until now, there is no well-developed method to obtain contact angles inside the GDLs. AlRatrout et al. developed an open-source code to compute local contact angles at triple-phase contact points from segmented micro-X-ray computed tomography (X-ray CT) images of porous rocks. We apply it, for the first time, to micro-X-ray CT images of water-filled commercial GDLs and compute local contact angles at internal GDL fiber-water-air triple-phase contact points. We obtain a state of mixed wettability (hydrophilic and hydrophobic) inside all GDL samples, with a broad range of contact angles, instead of one hydrophobic contact angle found from goniometer experiments. Lattice Boltzmann water transport simulations performed with these distributed contact angles produce results that are in better agreement with experimental data. We also obtain high-resolution X-ray photoelectron spectroscopy (XPS) data of the GDL samples and find that the concentration of oxide species correlates strongly with the measured hydrophilicity. The method introduced here can help rationally design GDLs and directly quantify their internal surface wettability that is needed for accurate predictions of their functionality in energy technology devices.

Unique selectivity trends of highly permeable PAP[5] water channel membranes.

Artificial water channels are a practical alternative to biological water channels for achieving exceptional water permeability and selectivity in a stable and scalable architecture. However, channel-based membrane fabrication faces critical barriers such as: (1) increasing pore density to achieve measurable gains in permeability while maintaining selectivity, and (2) scale-up to practical membrane sizes for applications. Recently, we proposed a technique to prepare channel-based membranes using peptide-appended pillar[5]arene (PAP[5]) artificial water channels, addressing the above challenges. These multi-layered PAP[5] membranes (ML-PAP[5]) showed significantly improved water permeability compared to commercial membranes with similar molecular weight cut-offs. However, due to the distinctive pore structure of water channels and the layer-by-layer architecture of the membrane, the separation behavior is unique and was still not fully understood. In this paper, two unique selectivity trends of ML-PAP[5] membranes are discussed from the perspectives of channel geometry, ion exclusion, and linear molecule transport.

"Where Does the Circle End?": Representation as a Critical Aspect of Reflection in Teaching Social and Behavioral Sciences in Medicine.

OBJECTIVE: This paper describes a reflective learning program within a larger curriculum on behavioral and social science that makes use of close reading, written representation of experience, discussion, and textual response. This response may in turn lead to further reflection, representation, and response in a circular pattern. A unique feature of this program is that it pays attention to the representation itself as the pivotal activity within reflective learning. Using the narrative methods that are the hallmark of this program, faculty writings were analyzed to characterize the essential benefits that derive from these practices. METHODS: In the context of a faculty development seminar on the teaching of behavioral and social sciences in medical curricula, a group of 15 faculty members wrote brief narratives of reflective learning experiences in which they had made use of the methods described above. Their responses were submitted to iterative close reading and discussion, and potential themes were identified. RESULTS: Four themes emerged: writing as attention to self, writing as attention to other, writing as reader/writer contract, and writing as discovery. In each instance, writing provides a new or deepened perspective, and in each case, the dividends for the writer are amplified by the narrative skills of those who read, listen, and respond. CONCLUSIONS: The narrative pedagogy described and modeled herein provides a potentially promising approach to teaching the social, cultural, behavioral, and interpersonal aspects of medical education and practice. Future research will deepen our understanding of the benefits and limitations of this pedagogy and expand our appreciation of its applications.

Breastfeeding and sexuality: professional advice literature from the 1970s to the present.

Since the 1970s, there has been a trend on the part of physicians and other health practitioners to promote breastfeeding in the United States, a movement that has not been as successful as hoped, since the majority of mothers in this country continue to feed their babies formula. Several socioeconomic factors are considered to be barriers to the success of breastfeeding promotion today. Yet, even among those who promote breastfeeding there exists a notable constraint in dealing with the issue of sexuality and breastfeeding. Indeed, as the female breast is eroticized in Western society, breastfeeding promotional messages have often exhibited a tacit conformity to social conventions regarding female sexuality. When analyzing selected works of advice literature written by health care practitioners from the 1970s to the present, it will be clear that breastfeeding promotional information often reflects dominant views of the sexuality of the female breast and her body.