Key parameters that influence the specific energy of electrochemical double-layer capacitors (EDLCs) are the double-layer capacitance and the operating potential of the cell. The operating potential of the cell is generally limited by the electrochemical window of the electrolyte solution, that is, the range of applied voltages within which the electrolyte or solvent is not reduced or oxidized. Ionic liquids are of interest as electrolytes for EDLCs because they offer relatively wide potential windows. Here, we provide a systematic study of the influence of the physical properties of ionic liquid electrolytes on the electrochemical stability and electrochemical performance (double-layer capacitance, specific energy) of EDLCs that employ a mesoporous carbon model electrode with uniform, highly interconnected mesopores (3DOm carbon). Several ionic liquids with structurally diverse anions (tetrafluoroborate, trifluoromethanesulfonate, trifluoromethanesulfonimide) and cations (imidazolium, ammonium, pyridinium, piperidinium, and pyrrolidinium) were investigated. We show that the cation size has a significant effect on the electrolyte viscosity and conductivity, as well as the capacitance of EDLCs. Imidazolium- and pyridinium-based ionic liquids provide the highest cell capacitance, and ammonium-based ionic liquids offer potential windows much larger than imidazolium and pyridinium ionic liquids. Increasing the chain length of the alkyl substituents in 1-alkyl-3-methylimidazolium trifluoromethanesulfonimide does not widen the potential window of the ionic liquid. We identified the ionic liquids that maximize the specific energies of EDLCs through the combined effects of their potential windows and the double-layer capacitance. The highest specific energies are obtained with ionic liquid electrolytes that possess moderate electrochemical stability, small ionic volumes, low viscosity, and hence high conductivity, the best performing ionic liquid tested being 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

In many commercially available and in-house-prepared reference electrodes, nanoporous glass frits (often of the brand named Vycor) contain the electrolyte solution that forms a salt bridge between the sample and the reference solution. Recently, we showed that in samples with low ionic strength, the half-cell potentials of reference electrodes comprising nanoporous Vycor frits are affected by the sample and can shift in response to the sample composition by more than 50 mV (which can cause up to 900% error in potentiometric measurements). It was confirmed that the large potential variations result from electrostatic screening of ion transfer through the frit due to the negatively charged surfaces of the glass nanopores. Since the commercial production of porous Vycor glass was recently discontinued, new materials have been used lately as porous frits in commercially available reference electrodes, namely frits made of Teflon, polyethylene, or one of two porous glasses sold under the brand names CoralPor and Electro-porous KT. In this work, we studied the effect of the frit characteristics on the performance of reference electrodes, and show that the unwanted changes in the reference potential are not unique to electrodes with Vycor frits. Increasing the pore size in the glass frits from the <10 nm into the 1 μm range or switching to polymeric frits with pores in the 1 to 10 μm range nearly eliminates the potential variations caused by electrostatic screening of ion transport through the frit pores. Unfortunately, bigger frit pores result in larger flow rates of the reference solution through the pores, which can result in the contamination of test solutions.

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This article describes an ongoing initiative of the Department of Chemistry (Chem. Dept.) at the University of Minnesota (UMN) to support the mental health of graduate students. With the increasing pressure on students to carry out novel research, publish articles, learn a broad range of skills, and look for career opportunities, the levels of stress, anxiety, and depression among graduate students are on the rise. For tackling these issues, the UMN Chem. Dept. has adopted an approach that heavily relies on the involvement of graduate students and student empowerment. This contribution describes the results of a collaboration between a student group (Community of Chemistry Graduate Students, CCGS), the director of graduate studies of the Chem. Dept., and mental health professionals at the UMN campus health service, to provide strategies for ensuring a welcoming and productive departmental climate. It describes the events that CCGS has hosted to help to improve the mental health of students, and raise awareness and stimulate open discussions about this topic. As an early intervention strategy, the UMN Chem. Dept. revised several policies to ensure that students receive frequent feedback from their advisors. Through the collaboration of the CCGS, UMN Chem. Dept., and UMN campus health service, a survey for the evaluation of mental health and stress factors in graduate studies was developed. Findings of the survey attest to the stigma associated with mental health, as more than 40% of the graduate students responded that they did not consider consulting with a therapist, counselor, or physician even when they felt that their health was affected by the level of stress in their lives. The results also show the importance of an open and friendly environment for students who struggle with stress and mental health, as they were most likely to approach a friend rather than advisor, counselor, or physician.