From batteries to agriculture, Stanford energy fellows' ingenuity illuminates

The first annual Stanford Energy Postdoctoral Fellowship Symposium opened with encouragement from Richard Swanson, founder of solar company SunPower and former Stanford University faculty member. "I find when I talk to students that they're very energizing, and I come away really pumped up," Swanson said, before playfully adding, "I hope you don't disappoint.”

Eight energy fellows presented their latest research results. Four Stanford professors, a Northwestern University professor, and Swanson gave mostly high-level observations about the future of sustainable, affordable, secure energy. The symposium demonstrated how inventive science becomes when combining disparate fields like batteries and carbon-neutral fuels, electric grids and markets, or plasma physics and agriculture. 

“Requiring new PhD’s to have at least two mentors in two different departments set the foundation for the program’s interdisciplinary structure, along with regular scientific interactions among all the fellows,” said Yi Cui, the faculty director of the postdoctoral fellowship, which he created in 2022 when he directed Stanford’s Precourt Institute for Energy.

Stolen electrons and solid-state batteries

Energy fellow John "Jack" Holoubek tackled two seemingly unrelated problems through electrolyte modification. CO₂ electrolyzers waste current by producing hydrogen instead of intended products. Grid-scale zinc batteries, meanwhile, produce unwanted hydrogen because water molecules steal electrons. In both cases, Holoubek’s solution is to modify the electrolyte, not the metal. 

For the CO2 electrolyzer, he replaced sodium cations with a trivalent aluminum complex to get the desired products instead of hydrogen efficiently. For the zinc batteries, Holoubek designed a new low-cost organic electrolyte to eliminate hydrogen generation.

If liquid electrolytes cause headaches, why not ditch them? That is Yukio  Cho’s wager for using a solid electrolyte to advance lithium-sulfur batteries, the theoretical energy density of which could eclipse today’s lithium-ion cells. Historically, solid-state lithium-sulfur batteries have faced challenges, most notably the sluggish chemical movement that hampers their ability to store and release energy quickly.

Cho pinpointed an often-overlooked interfacial issue that was dragging down reaction rates. A simple vacuum treatment removed obstructive surface layers that clogged up electron and ion pathways, enabling thick, high-loading cathodes to retain 80% of their capacity after 500 fast-charge cycles at room temperature.

Memory walls and model collaborations

Electricity is spent – often wastefully – shuttling bits inside AI chips.  Fabia Farlin Athena aims to alleviate the memory wall erected by slow off-chip dynamic-random-access memory, slowing the work of the speedy processors used for AI. To maintain data corruption or loss, DRAM must periodically refresh its memory storage by reading the data and then rewriting it. Athena looked at two-transistor gain-cell memory that can be stacked directly atop logic layers, but a stumbling block remained: threshold voltage drift in oxide semiconductors operating at 185°F. (85°C.)

Athena inserted an aluminum oxide layer that nudges the threshold 450 millivolts in the right direction without hurting electron mobility. Leakage plummets, and simulations show a 50,000-fold cut in refresh energy, which would accelerate compute time while avoiding all that wasted electricity.

Lisa Rennels, meanwhile, posed that innovations in open-source software and reproducible science can be as valuable as physical innovations. Her Julia-based Mimi language helps economists collaborate and improve integrated assessment models without having to wrestle multiple languages and environments. However, her user studies reveal that even well-designed domain specific languages can break, and that understanding the user experience is key for their success.

Grid markets and dendrites

Cong Chen researches integrating energy storage into power grids with high levels of unpredictable wind and solar output. Owners of large battery systems buy electricity when prices are low, sell when prices rise, and quickly respond to sudden power imbalances. 

Chen developed a fast, market-friendly optimization rule she named “the equal decremental cost rule.” She hopes it helps grid operators schedule and price energy storage more efficiently while stabilizing the system. Chen has also designed real-time auctions for residential neighborhoods where electric vehicles, home batteries, and rooftop solar compete for limited local power line capacity.

To prevent chemicals from forming crystallized spikes – or dendrites – that can weaken a battery or even cause it to combust, Yecun  Wu turns hexagonal boron nitride defects into nanoscale periscopes. When hit by laser light, these defects fluoresce, shifting color when a single lithium ion parks nearby. By tracking these millisecond-cadence blinks with spectral fingerprints, Wu can precisely detect the behavior of individual ions.

Biology’s role

Securing food for a growing world population requires high crop yields and healthy soils. Current chemical fertilizer production is energy-intensive, and inefficient application leads to nitrous oxide emissions from soils. Luca Vialetto envisions decentralized fertilizer production from ionized gases, also called plasmas, powered by renewable electricity. When plasmas contact water, they create chemical compounds that enhance plant growth while reducing irrigation requirements and controlling pathogens. Vialetto explores computational models to understand and optimize this technology for integration into food production.

Lev Tsypin focuses on organisms that are naturally suited for sustainability applications. He is investigating genetic engineering tools for Botryococcus braunii, a green alga that has evolved to produce oils that may be used in place of petroleum. In the lab of Prof. Ellen Yeh, Tsypin also works with diatoms, which are evolutionarily poised for biomanufacturing applications, particularly sustainable fertilizer (ammonia) and nutraceuticals (Omega-3 fatty acids).

Broad view

The four featured talks by professors and Swanson provided the Stanford energy fellows with wider contexts for their work. Stanford Professor Sally Benson's California modeling revealed that an all-renewables plus batteries grid could double the state's power system costs. However, adding clean firm power – nuclear, hydrogen, or natural gas with carbon capture – reduces the premium to just 20%.

Northwestern University Professor Ted Sargent argued that cheap electrons can no longer be taken for granted as AI workloads balloon faster than aggressive renewable buildouts can accommodate. Meanwhile, Stanford polymer physicist Danielle Mai advances circular economies by making waste plastic from 3D printing recyclable through reversible bonds resembling zipper teeth. 

“This was an exciting day, with every presentation followed by engaged audience Q&A, including a lively lunch-time poster session featuring 10 additional energy fellows,” said the program’s director, Audrey Yau. "When our final fellows from our third cohort arrive on campus this summer, we will have a community of 25 fellows and two alums, plus all their faculty mentors. With applications for the fourth cohort opening on July 1, our community will continue to grow."

Cui is also faculty director of the Sustainability Accelerator at the Stanford Doerr School of Sustainability, co-director of the Precourt Institute's StorageX Initiative, senior fellow at the Precourt Institute and the Stanford Woods Institute for the Environment, and a professor in the departments of Materials Science & Engineering in the School of Engineering, of Energy Science & Engineering in the Doerr School, and of Photon Science at SLAC National Accelerator Laboratory. Yau is also the director of the postdoctoral fellowship at the Sustainability Accelerator. The Precourt Institute and the Woods Institute are part of the Stanford Doerr School of Sustainability.

The Stanford Energy Postdoctoral Fellowship is sponsored by Stanford’s Precourt Institute for Energy, TomKat Center for Sustainable Energy, Bits & Watts Initiative, and StorageX Initiative.