The Superpowers of Hydrogen Atoms
Hydrogen is simple, and hydrogen is everywhere. It makes up ~90% of the atoms in the universe and 63% of the atoms in our bodies. Hydrogen atoms are simple in that they consist of a single proton with the option of no electrons (H+, also called a proton), one electron (H0, a neutral hydrogen atom), or two electrons (H-, hydride). Despite its simplicity and omnipresence, scientists have only begun to grasp how hydrogen interacts with other elements due to its tiny mass and elusive nature. The Hydrogen in Energy and Information Sciences (HEISs) Energy Frontier Research Center (EFRC) is a new EFRC that aims to understand and control the interactions between all forms of hydrogen atoms and solid materials. Led by Sossina M. Haile of Northwestern University, HEISs consists of a multi-disciplinary team of scientists with complementary expertise across six institutions .
Understanding how hydrogen atoms interact with materials — whether hydrogen moves through the bulk or interacts with the surface — is a bottleneck in developing better materials to improve energy technologies and energy-efficient computing. These two use-inspired areas are the context within which HEISs will investigate hydrogen’s behavior and seek to elucidate the fundamental interactions critical to material function.
Many of the fundamental questions HEISs aims to answer revolve around how certain controllable parameters dynamically influence hydrogen’s identity and interactions with solid materials. These parameters can be intrinsic to the material (defects, grain boundaries, strain, and band gap) or extrinsic (pressure, light, and electric fields). Many open questions in both realms remain. For instance, do point defects in materials, such as substitutional and vacancy defects, act as “traps” and hinder bulk transport? Do extended defects, such as dislocations and grain boundaries, act as high-mobility pathways? How does the presence of defects affect material behavior, and does it depend on the location of the defect, either in the bulk or on the surface? Can the identity and dynamics of the hydrogen atoms be tuned through modulating intrinsic properties of the materials and external stimuli?
The scientists in HEISs are well positioned to make headway toward answering these longstanding questions using (1) specialized techniques such as neutron scattering and nuclear magnetic resonance to probe elusive hydrogen atoms, and (2) equipment to probe how external parameters impact hydrogen within inorganic materials. This new understanding can be used to design high performance materials for energy and information sciences.
In the energy realm, electrochemical energy devices are used to convert chemical energy to electricity and vice versa. A fuel cell device converts chemical energy to electricity, and an electrolyzer converts electricity to chemical energy. The heart of both fuel cells and electrolyzers is typically an electrolyte membrane that allows proton transport while blocking electron transport. The electrolyte membrane is sandwiched between two electrode catalyst layers whose role is to split hydrogen atoms into protons and electrons, or combine protons and electrons to form hydrogen. For aqueous low temperature (<100°C) devices, polymer membranes fit the bill, but for higher temperature gas-phase systems (~400 to 600°C), ceramic membrane materials are more suitable [2–4]. HEISs aims to understand how the uptake, transport, and discharge of hydrogen across electrode–electrolyte interfaces and through ceramic electrolytes can be tuned using the intrinsic and extrinsic parameters shown in Figure 2.
In the realm of information sciences, the amount of electricity used by computers, data centers, and communication devices is increasing so quickly that by 2040, the world may not be able to produce enough electricity to keep up with demand . Given this growing demand, HEISs aims to study transistor-like programmable resistors for analog computing. It was recently discovered that intercalating a transistor-like synapse, called a programmable resistor, with hydrogen atoms increases its electrical conductivity. The programmable resistor exhibited excellent energy efficiencies when protons modulated its electrical conductivity with nanosecond frequency [6,7]. The source of protons was provided by palladium, which exhibits a unique ability to uptake unusually large amounts of hydrogen atoms to reversibly form palladium hydride . Just like in the energy realm, HEISs aims to understand how modulating the intrinsic and extrinsic parameters in Figure 2 can impact the conductivity and energy efficiency of programmable resistors.
With energy and climate change as heiß topics in scientific research today, HEISs is equipped and ready to propel the understanding of hydrogen atoms within inorganic materials. Look forward to future issues as we discuss the challenges of detecting hydrogen atoms and the techniques researchers at HEISs will use to track hydrogen atoms in action!
 Center for Hydrogen in Energy and Information Sciences (HEISs), https://heiss.northwestern.edu/
 Choi, Sihyuk, Timothy C. Davenport, and Sossina M. Haile. "Protonic ceramic electrochemical cells for hydrogen production and electricity generation: exceptional reversibility, stability, and demonstrated faradaic efficiency." Energy & Environmental Science 12.1 (2019): 206-215.
 Duan, Chuancheng, et al. "Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production." Nature Energy 4.3 (2019): 230-240.
 Herradon, Carolina, et al. "Proton-conducting ceramics for water electrolysis and hydrogen production at elevated pressure." Frontiers in Energy Research (2022): 1546.
 Belkhir, Lotfi, and Ahmed Elmeligi. "Assessing ICT global emissions footprint: Trends to 2040 & recommendations." Journal of cleaner production 177 (2018): 448-463.
 Yao, Xiahui, et al. "Protonic solid-state electrochemical synapse for physical neural networks." Nature communications 11.1 (2020): 3134.
 Onen, Murat, et al. "Nanosecond protonic programmable resistors for analog deep learning." Science 377.6605 (2022): 539-543.
 Adams, Brian D., and Aicheng Chen. "The role of palladium in a hydrogen economy." Materials today 14.6 (2011): 282-289.
The author thanks Paul Chery, Sossina Haile, Nancy Washton, Jeffrey Holmes, Xavier Krull, and Linu Malakkal for proofreading and comments.