The Northeastern University Chemical Engineering awards ceremony was today. Adam Ekenseair and I both received an award made possible by alumnus Richard Sioui, for “going beyond the normal expectations of an instructor to make a positive impact on students’ education and careers.” I was honored to meet Dr. Sioui and his wife Mary.
Introducing our lab group, seen here at our second ever Friday afternoon group meeting. From left to right, Ben Howell, Matthew Kim, and Zhicheng Lu. All devouring electrochemistry and coming up to speed. The future is truly bright.
I’ve been mulling over what to call the group. “Gallaway Group” would be fine, but as is the fashion these days perhaps it should be something both punchier and more descriptive, with an acronym involved. The Complex Electrochemical Systems Lab (CESL, pronounced “sessil” if you like) is what told Northeastern I might do before I got here, so maybe that’s it. What do I mean by complex? All electrochemistry is complex from a certain point of view. But here I specifically mean systems when multiple phenomena are important throughout the regime of operation, such as two kinds of diffusion (e.g. in a solid crystal and in an electrolyte) or three kinds of kinetics (e.g. both substrate and mediator of an enzyme, also with mediator electrode kinetics). To that you could say “That means all real battery or fuel cell systems are complex.” To which I would say “Yes that’s right.” But this is a defined viewpoint, a worldview, and those are good to set down for all to see. It tells you we will always be trying to break down a complex system, and then build it back up … engineered to be better of course.
The Brookhaven National Lab newsroom has a nice profile about the work we did at the SRX beamline as one of the first user groups to work there. As soon as beamtime proposals were being accepted in 2015, we submitted one to study the mechanism of a new battery formulation we had just discovered (and which has since been published). Since then we made three trips to collect data, all of which were insightful. I just gave a preliminary account of what we found in a talk at ECS, and I hope to have the paper out in the fall.
In the article I tried to lay out why the SRX beamline was the perfect tool to do what we wanted, electrochemically. If you’re interested in the simultaneous oxidation/reduction of several different elements (in our case Mn, Bi, Cu) SRX lets you map them spatially and also sample their redox states on the fly.
Many thanks to Laura Mgrdichian who interviewed me and Gautam and wrote the article. She started by asking “What draws you to this research?” and I’m always happy to answer that. Electrochemistry is instrumental in getting society to the ultimate goal of energy sustainability.
I’m happy to announce that beginning this fall I’ll be the DiPietro Assistant Professor of Chemical Engineering at Northeastern University. There I’ll continue working to improve kinetics and transport within complex electrochemical systems. You can expect batteries, phase changes, and synchrotron science, as well as some new tricks. It’s an understatement to say I’m looking forward to it. See you soon.
Some exciting news: we have a new paper out in Nature Communications featuring a deep cycling manganese dioxide (MnO2) cathode. This cathode is aqueous, operating for thousands of cycles in KOH electrolyte, at essentially the full 2-electron capacity of MnO2, which is 617 mAh/g-MnO2. MnO2 is abundant, inexpensive, and non-toxic, making it an ideal basis material for large-scale batteries at the scale of the power grid. Batteries on this scale will make widespread use of solar and wind power possible in the future. Because the electrolyte is water-based, the resulting battery is inherently safer than Li-ion, which relies on a highly flammable electrolyte. Fires caused by Li-ion batteries in small devices like cell phones are a generally accepted risk, but for massive stationary batteries located in power grid infrastructure the risk assessment recommends using a safer, water-based battery chemistry.
The paper title is Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries, and the innovation that makes everything possible is intercalating copper (Cu) into bismuth-modified δ-MnO2 (birnessite). Bismuth-birnessite was discovered by Ford Motor Company in the 1980s, but it was never known how to use it at high areal capacity. The first five cycles of a cathode with no copper (a) and with copper (b) are shown below. Without copper the cathode failed by the third cycle.
Gautam Yadav discovered this copper intercalation here at the CUNY Energy Institute during the final year of our ARPA-E project. The reason it is a big discovery is this: Bi-birnessite will cycle nicely under some conditions, for example at low mass loading or with a very thin electrode, i.e. situations with low areal capacity. In contrast, we achieved both high cycle life and very high areal capacity. Areal capacity is measured in mAh/cm2, and achieving high areal capacity is critical for packing a lot of electrodes together with high energy density. Any practical battery requires high areal capacity (as opposed to batteries meant as academic exercises or low-level proofs of concept).
The plot above puts areal capacity in context. One recent report (ref 62) achieved 5,000 cycles, but at a small areal capacity of 1 mAh/cm2. Another report (ref 44) successfully achieved 26 mAh/cm2, but with only 60 recharging cycles. By using Cu-intercalated MnO2 we achieved 6,000 cycles at 2.5 mAh/cm2 and 1,000 cycles at 28 mAh/cm2. Battery modeling suggests this opens up a design pathway to 200 Wh/L, equal to the energy density of some kinds of Li-ion battery, for an aqueous Zn-MnO2 battery.