Bimetallic iron–nickel-based nanocatalysts are perhaps the most active for the oxygen evolution reaction (OER) in alkaline electrolytes. Recent developments in literature have suggested that the ratio of iron and nickel in Fe–Ni thin films plays an essential role in the performance and stability of the catalysts. In this work, the metallic ratio of iron to nickel was tested in alloy bimetallic nanoparticles. Similar to thin films, nanoparticles with iron–nickel atomic compositions where the atomic iron percentage is ≤50% outperformed nanoparticles with iron–nickel ratios of >50%. Nanoparticles of Fe20Ni80, Fe50Ni50, and Fe80Ni20 compositions were evaluated and demonstrated to have overpotentials of 313, 327,, and 364 mV, respectively, at a current density of 10 mA/cm2. While the Fe20Ni80 composition might be considered to have the best OER performance at low current densities, Fe50Ni50 was found to have the best current density performance at higher current densities, making this composition particularly relevant for electrolysis conditions. However, when stability was evaluated through chronoamperometry and chronopotentiometry, the Fe80Ni20 composition resulted in the lowest degradation rates of 2.9 μA/h and 17.2 μV/h, respectively. These results suggest that nanoparticles with higher iron and lower nickel content, such as the Fe80Ni20 composition, should be still taken into consideration while optimizing these bimetallic OER catalysts for overall electrocatalytic performance. Characterization by electron microscopy, diffraction, and X-ray spectroscopy provides detailed chemical and structural information on as-synthesized nanoparticle materials.

Bimetallic iron−nickel oxide/hydroxide (FeNiO(H) x ) nanocatalysts have emerged as nonprecious metal candidates for alkaline oxygen evolution reaction (OER) electrocatalysis. However, there are still significant open questions regarding the role of electrocatalyst synthesis route, and the resulting electrocatalyst morphology and nanoscale structure, in determining the operando atomicscale structure when subjected to the faradic OER voltage environment. Herein, we report on two nanoparticle FeNiO(H) x electrocatalysts and their different chemical structures using operando X-ray absorption spectroscopy (XAS) studies at relevant OER conditions. The two bimetallic nanoparticle electrocatalysts were synthesized using aqueous (NP-aq) vs oil-based (NP-oil) synthesis routes but resulted in compositionally similar surface chemistry as-synthesized. Operando XAS results suggest that Ni oxidizes from the initial +2 oxidation state to +3/+4 state reminiscent of the transformation of α-Ni(OH) 2 to γ-NiOOH; the oxidation state change is voltage-dependent and occurs in both NP-aq and NP-oil nanoparticles. There does not appear to be an oxidation state change for Fe, but the Fe coordination environment does change with voltage. The NP-aq nanoparticles resulted in Fe coordination transitions between Fe 3+ T d , observed in as-synthesized and 0.8−0.9 V vs Ag/AgCl conditions, and Fe 3+ O h , observed at 0 V vs Ag/AgCl, while the NP-oil nanoparticles resulted in a largely stable Fe 3+ O h coordination with more subtle changes in the coordination environment. The voltage dependence of this Fe coordination transition is nanoparticle-dependent, with NP-aq nanoparticles transitioning dramatically at 0.7 V vs Ag/AgCl but NP-oil nanoparticles transitioning slowly starting at 0.1 V vs Ag/ AgCl. Additionally, a shortening of both the Fe−O and Ni−O bond distances occurs for both nanoparticle materials, but the magnitude of change is different for NP-aq vs NP-oil, suggesting that the nanoparticle structures result in unique changes under applied potential. Extended X-ray absorption fine structure (EXAFS) analysis showed distinct chemical environments for the Fe species of NP-aq vs NP-oil, metallic Fe and Ni character in NP-aq, and Ni largely in a hydroxide phase for both nanoparticles. NP-aq results in improved activity and stability during OER, as compared to NP-oil, suggesting that the Fe 3+ O h → T d transition, metallic core, and a predominant Fe-incorporated Ni(OH) 2 phase in the shell are important for OER performance. This study highlights that both the electrochemical environment and the as-synthesized morphology of nanoparticle electrocatalysts are important in determining the operational chemical structures and structure−performance relationships.

The 3-D morphology plays a key role in the optimization of the electrocatalytic activity and stability of nanocatalysts for the OER.

The antimicrobial activity and mechanism of silver ions (Ag+) have gained broad attention in recent years. However, dynamic studies are rare in this field. Here, we report our measurement of the effects of Ag+ ions on the dynamics of histone-like nucleoid-structuring (H-NS) proteins in live bacteria using single-particle-tracking photoactivated localization microscopy (sptPALM). It was found that treating the bacteria with Ag+ ions led to faster diffusive dynamics of H-NS proteins. Several techniques were used to understand the mechanism of the observed faster dynamics. Electrophoretic mobility shift assay on purified H-NS proteins indicated that Ag+ ions weaken the binding between H-NS proteins and DNA. Isothermal titration calorimetry confirmed that DNA and Ag+ ions interact directly. Our recently developed sensing method based on bent DNA suggested that Ag+ ions caused dehybridization of double-stranded DNA (i.e., dissociation into single strands). These evidences led us to a plausible mechanism for the observed faster dynamics of H-NS proteins in live bacteria when subjected to Ag+ ions: Ag+-induced DNA dehybridization weakens the binding between H-NS proteins and DNA. This work highlighted the importance of dynamic study of single proteins in live cells for understanding the functions of antimicrobial agents in bacteria. IMPORTANCE As so-called “superbug” bacteria resistant to commonly prescribed antibiotics have become a global threat to public health in recent years, noble metals, such as silver, in various forms have been attracting broad attention due to their antimicrobial activities. However, most of the studies in the existing literature have relied on the traditional bioassays for studying the antimicrobial mechanism of silver; in addition, temporal resolution is largely missing for understanding the effects of silver on the molecular dynamics inside bacteria. Here, we report our study of the antimicrobial effect of silver ions at the nanoscale on the diffusive dynamics of histone-like nucleoid-structuring (H-NS) proteins in live bacteria using single-particle-tracking photoactivated localization microscopy. This work highlights the importance of dynamic study of single proteins in live cells for understanding the functions of antimicrobial agents in bacteria.