Building upon the
- Award ID(s):
- 1845531
- NSF-PAR ID:
- 10360533
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Bacillus subtilis endospore‐mediated forsterite dissolution experiments were performed to assess the effects of cell surface reactivity on Mg isotope fractionation during chemical weathering. Endospores present a unique opportunity to study the isolated impact of cell surface reactivity because they exhibit extremely low metabolic activity. In abiotic control assays,24Mg was preferentially released into solution during forsterite dissolution, producing an isotopically light liquid phase (δ26Mg = −0.39 ± 0.06 to −0.26 ± 0.09‰) relative to the initial mineral composition (δ26Mg = −0.24 ± 0.03‰). The presence of endospores did not have an apparent effect on Mg isotope fractionation associated with the release of Mg from the solid into the aqueous phase. However, the endospore surfaces preferentially adsorbed24Mg from the dissolution products, which resulted in relatively heavy aqueous Mg isotope compositions. These aqueous Mg isotope compositions increased proportional to the fraction of dissolved Mg that was adsorbed, with the highest measured δ26Mg (−0.08 ± 0.07‰) corresponding to the highest degree of adsorption (~76%). The Mg isotope composition of the adsorbed fraction was correspondingly light, at an average δ26Mg of −0.49‰. Secondary mineral precipitation and Mg adsorption onto secondary minerals had a minimal effect on Mg isotopes at these experimental conditions. Results demonstrate the isolated effects of cell surface reactivity on Mg isotope fractionation separate from other common biological processes, such as metabolism and organic acid production. With further study, Mg isotopes could be used to elucidate the role of the biosphere on Mg cycling in the environment. -
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Abstract The electrochemical ammonia oxidation to dinitrogen as a means for energy and environmental applications is a key technology toward the realization of a sustainable nitrogen cycle. The state-of-the-art metal catalysts including Pt and its bimetallics with Ir show promising activity, albeit suffering from high overpotentials for appreciable current densities and the soaring price of precious metals. Herein, the immense design space of ternary Pt alloy nanostructures is explored by graph neural networks trained on ab initio data for concurrently predicting site reactivity, surface stability, and catalyst synthesizability descriptors. Among a few Ir-free candidates that emerge from the active learning workflow, Pt3Ru-M (M: Fe, Co, or Ni) alloys were successfully synthesized and experimentally verified to be more active toward ammonia oxidation than Pt, Pt3Ir, and Pt3Ru. More importantly, feature attribution analyses using the machine-learned representation of site motifs provide fundamental insights into chemical bonding at metal surfaces and shed light on design strategies for high-performance catalytic systems beyond the
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Abstract A fundamental understanding of the enantiospecific interactions between chiral adsorbates and understanding of their interactions with chiral surfaces is key to unlocking the origins of enantiospecific surface chemistry. Herein, the adsorption and decomposition of the amino acid proline (Pro) have been studied on the achiral Cu(110) and Cu(111) surfaces and on the chiral Cu(643)
R&S surfaces. Isotopically labelled 1‐13C‐l‐ Pro has been used to probe the Pro decomposition mechanism and to allow mass spectrometric discrimination ofd ‐Pro and 1‐13C‐l ‐Pro when adsorbed as mixtures. On the Cu(111) surface, X‐ray photoelectron spectroscopy reveals that Pro adsorbs as an anionic species in the monolayer. On the chiral Cu(643)R&S surface, adsorbed Pro enantiomers decompose with non‐enantiospecific kinetics. However, the decomposition kinetics were found to be different on the terraces versus the kinked steps. Exposure of the chiral Cu(643)R&S surfaces to a racemic gas phase mixture ofd ‐Pro and 1‐13C‐l ‐Pro resulted in the adsorption of a racemic mixture; i.e., adsorption is not enantiospecific. However, exposure to non‐racemic mixtures ofd ‐Pro and 1‐13C‐l ‐Pro resulted in amplification of enantiomeric excess on the surface, indicative of homochiral aggregation of adsorbed Pro. During co‐adsorption, this amplification is observed even at very low coverages, quite distinct from the behavior of other amino acids, which begin to exhibit homochiral aggregation only after reaching monolayer coverages. The equilibrium adsorption ofd ‐Pro and 1‐13C‐l ‐Pro mixtures on achiral Cu(110) did not display any aggregation, consistent with prior scanning tunneling microscopy (STM) observations ofdl ‐Pro/Cu(110). This demonstrates convergence between findings from equilibrium adsorption methods and STM experiments and corroborates formation of a 2D random solid solution. -
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Abstract Although interfacial solvation plays an important role in determining carbon dioxide reduction (CO2R) kinetics, present understanding of the potential dependent properties of the electrochemical double layer under conditions relevant for CO2R remains limited. This article summarizes the development and recent applications of plasmon‐enhanced vibrational sum frequency generation (VSFG) spectroscopy to study the effects of cation hydration and interfacial solvation on CO2R using CO as a vibrational Stark reporter. Results show that electrolyte cations retain their entire solvation shell upon adsorption to inactive sites, while active sites retain only a single water layer between the gold surface and the cation. Measurements also show that the total interfacial electric field can be separated into two contributions: one from the electrochemical double layer (Stern field) and another from the polar solvation environment (Onsager field). Surprisingly, correlating VSFG spectra with reaction kinetics reveals that it is the solvation‐mediated Onsager field that governs the chemical reactivity at the electrode/electrolyte interface. Measuring the interfacial water spectra during electrocatalysis also provides evidence for the proton source during H2evolution, which competes with CO2R in aqueous electrolyte. These findings highlight the importance of directly probing cation hydration and interfacial solvation, which mediates reaction kinetics at electrochemical interfaces.
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Abstract Transition metal‐nitrogen‐carbon materials with atomically dispersed active sites are promising catalysts for oxygen evolution reaction (OER) since they combine the strengths of both homogeneous and heterogeneous catalysts. However, the canonically symmetric active site usually exhibits poor OER intrinsic activity due to its excessively strong or weak oxygen species adsorption. Here, a catalyst with asymmetric MN4sites based on the 3‐s‐triazine of g‐C3N4(termed as a‐MN4@NC) is proposed. Compared to symmetric, the asymmetric active sites directly modulate the oxygen species adsorption via unifying planar and axial orbitals (d
x 2‐y 2, dz 2), thus enabling higher OER intrinsic activity. In Silico screening suggested that cobalt has the best OER activity among familiar nonprecious transition metal. These experimental results suggest that the intrinsic activity of asymmetric active sites (179 mV overpotential at onset potential) is enhanced by 48.4% compared to symmetric under similar conditions. Remarkably, a‐CoN4@NC showed excellent activity in alkaline water electrolyzer (AWE) device as OER catalyst, the electrolyzer only required 1.7 V and 2.1 V respectively to reach the current density of 150 mA cm−2and 500 mA cm−2. This work opens an avenue for modulating the active sites to obtain high intrinsic electrocatalytic performance including, but not limited to, OER.
