Hector D. Abruna

Precious-metal-free spinel oxide electrocatalysts are promising candidates for catalyzing the oxygen reduction reaction (ORR) in alkaline fuel cells. In this theory-driven study, we use joint density functional theory (JDFT) in tandem with supporting electrochemical measurements to identify a novel theoretical pathway for the ORR on cubic Co3O4 nanoparticle electrocatalysts, which aligns more closely with experimental results than previous models. The new pathway employs the cracked adsorbates *(OH)(O) and *(OH)(OH), which, through hydrogen bonding, induce spectator surface *H. This results in an onset potential closely matching experimental values, in stark contrast to the traditional ORR pathway, which keeps adsorbates intact and overestimates the onset potential by 0.7 V. Finally, we introduce electrochemical strain spectroscopy (ESS), a groundbreaking strain analysis technique. ESS combines ab initio …

Hydrogen fuel cells have drawn increasing attention as one of the most promising next-generation power sources for future automotive transportation. Developing efficient, durable, and low-cost electrocatalysts, to accelerate the sluggish oxygen reduction reaction (ORR) kinetics, is urgently needed to advance fuel cell technologies. Herein, we report on metal–organic frameworks-derived nonprecious dual metal single-atom catalysts (SACs) (Zn/Co–N–C), consisting of Co–N4 and Zn–N4 local structures. These catalysts exhibited superior ORR activity with a half-wave potential (E1/2) of 0.938 V versus RHE (reversible hydrogen electrode) and robust stability (ΔE1/2 = −8.5 mV) after 50k electrochemical cycles. Moreover, this remarkable performance was validated under realistic fuel cell working conditions, achieving a record-high peak power density of ∼1 W cm–2 among the reported SACs for alkaline fuel cells …

Encapsulating an electrocatalytic material with a semi-permeable, nanoscopic oxide overlayer offers a promising approach to enhancing its stability, activity, and/or selectivity compared to an unencapsulated electrocatalyst. However, applying nanoscopic oxide encapsulation layers to high surface area electrodes, such as nanoparticle-supported porous electrodes is a challenging task. This study demonstrates that the recently developed condensed layer deposition (CLD) method can be used for depositing nanoscopic (sub-10 nm thick) titanium dioxide (TiO2) overlayers onto high surface area platinized carbon foam electrodes. Characterization of the overlayers by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) showed that the films are amorphous, while X-ray photoelectron microscopy confirmed that they exhibit a TiO2 stoichiometry. Electrodes were also characterized by hydrogen underpotential deposition (Hupd) and carbon monoxide (CO) stripping, demonstrating that the Pt electrocatalysts remain electrochemically active after encapsulation. Additionally, copper underpotential deposition (Cuupd) measurements revealed that TiO2 overlayers are effective at blocking Cu2+ from reaching the TiO2/Pt buried interface and were used to estimate that between 43-98% of Pt surface sites were encapsulated. Overall, this study shows that CLD is a promising approach for depositing nanoscopic protective overlayers on high surface area electrodes.

Spinel oxides such as ternary cobalt manganese spinel oxides (CMOs) are promising electrocatalysts for oxygen reduction reaction (ORR) in anion exchange membrane fuel cells. Current efforts to enhance fuel cell cathode performance predominantly focus on tuning the ORR activity through the chemical and crystallographic engineering of the active material. However, the impact of ink formulation and film homogeneity on fuel cell performance remains poorly understood and under-investigated. Here we show that the deliberate retention of organic ligands can enhance the performance of a CMO/C composite by improving its film homogeneity. Surprisingly, retaining the organic ligands can optimize the catalyst–ionomer affinity and subsequent film homogeneity of this system, thus enhancing its fuel cell peak power density from 0.8 W/cm2 to 1.2 W/cm2. We demonstrate this effect by pre- and postsynthetic …

Oxides containing metals or metalloids from the p block of the periodic table (eg, In, Sn, Sb, Pb, and Bi) are of technological interest as transparent conductors and light absorbers for solar-energy conversion due to the tunability of their electronic conductivity and optical absorption. Comparatively, these oxides have found limited applications in hydrogen photoelectrolysis, primarily due to their high electronegativity, which impedes electron transfer for reducing protons into hydrogen. We have shown recently that inserting s-block cations into p-block metal oxides is effective at lowering electronegativities while affording further control of band gaps. Here, we explain the origins of this dual tunability by demonstrating the mediator role of s-block cations in modulating orbital hybridization while not contributing to frontier electronic states. From this result, we carry out a comprehensive computational study of 109 ternary …

Green hydrogen produced via photocatalysis is a promising sustainable energy source. However, many of the known water-splitting photoactive semiconductors are costly or of low efficiency due to their high electronegativity which impedes the transfer of electrons from the catalyst to chemisorbed/hydrated protons. To address this issue and expand the list of known water-splitting photocatalysts, we build on previous studies which showed via data-intensive screening that inserting pre-transition (s-block) metals in binary metal oxides can lower electronegativity while maintaining appealing light absorption properties. Starting from a family of post-transition (p-block) metal oxides used in optoelectronics, we analyze how adding pre-transition metals in these materials impacts the electronic couplings between their constituents and may improve their photocatalytic properties. Then, we screen 109 of these ternary metal …

The electrochemical reduction of CO2 presents an attractive opportunity to not only valorize CO2 as a feedstock for chemical products but also to provide a means to effectively store renewable electricity in the form of chemical bonds. The recent surge of experimental and computational studies of electrochemical CO2 reduction (ECR) has brought about significant scientific and technological advances. Yet, considerable gaps in our understanding of and control over the reaction mechanism persist, in particular for the formation of products. Moreover, while theoretical and computational studies have proposed many candidate reaction pathways, comprehensively reconciling these models with experimental observations remains challenging and elusive. The conventional electrochemical analysis of catalyst activity and selectivity generally relies on steady-state measurements. In a departure from this convention, we …

While certain ternary spinel oxides have been well-explored with colloidal nanochemistry, notably the ferrite spinel family, ternary manganese (Mn)-based spinel oxides have not been tamed. A key composition is cobalt (Co)-Mn oxide (CMO) spinel, CoxMn3–xO4, that, despite exemplary performance in multiple electrochemical applications, has few reports in the colloidal literature. Of these reports, most show aggregated and polydisperse products. Here, we describe a synthetic method for small, colloidally stable CMO spinel nanocrystals with tunable composition and low dispersity. By reacting 2+ metal-acetylacetonate (M(acac)2) precursors in an amine solvent under an oxidizing environment, we developed a pathway that avoids the highly reducing conditions of typical colloidal synthesis reactions; these reducing conditions typically push the system toward a monoxide impurity phase. Through surface chemistry …