Designing Pt-based electrocatalysts with high surface energy

The reactivity of an electrocatalyst depends strongly on its surface structure. Pt-based electrocatalysts of nanocrystals (NCs) enclosed with high-index facets contain a large density of catalytically active sites formed from step and kink atoms on the facets and exhibit intrinsically superior activity. However, the Pt-based NCs of high-index facets do possess a high surface energy and are thermodynamically metastable, leading to a big challenge in their shape-controlled synthesis. To overcome the challenge, kinetic–thermodynamic control of crystal growth is indispensable and is currently realized mainly by electrochemical methods and surfactant-based wet chemical approaches. This Perspective reviews recent progresses in Pt-based electrocatalysts of monometallic and bimetallic NCs of high surface energy with different morphologies of convex or concave tetrahexahedron, trapezohedron, trisoctahedron, hexoctahedron, etc. Remarkable electrocatalytic performance of these NCs has been demonstrated. Despite the considerable progress already made, the electrocatalysts of NCs with high surface energy still hold significant future opportunities in both fundamental understanding and practical applications

Comparative investigation of CO2 and oxygen reduction on Fe/N/C catalysts

Fe/N/C catalysts have been investigated as promising non-noble metal catalysts for both CO2 reduction reaction (CO2RR) and oxygen reduction reaction (ORR). However, it is unclear whether both reactions hold the same active sites. In this study, the Fe/N/C catalysts were subjected to oxidation treatment in O2 at different temperatures to tune the reactivity. It was found that the oxidation treatment exhibits inverse effects on the CO2RR and ORR. The CO2RR activity was enhanced while ORR activity was suppressed after the oxidation treatment at temperatures from 80 to 240 °C. This result indicates that CO2RR and ORR occur at different active sites. Furthermore, it was evidenced that pyrrolic N increases significantly upon the oxidation treatment, similar to the variation tendency of the CO2RR activity, which suggests that pyrrolic N is highly relevant to the CO2RR on Fe/N/C catalysts

Pd nanocrystals with continuously tunable high-index facets as a model nanocatalyst

Knowledge of the structure–reactivity relationship of catalysts is usually gained through using well-defined bulk single-crystal planes as model catalysts. However, there exists a huge gap between bulk single-crystal planes and practical nanocatalysts in terms of size, structural complexity, and local environment. Herein, we efficiently bridged this gap by developing a model nanocatalyst based on nanocrystals with continuously tunable surface structures. Pd nanocrystals with finely tunable facets, ranging from a flat {100} low-index facet to a series of {hk0} high-index facets, were prepared by an electrochemical square-wave potential method. The validity of the Pd model nanocatalyst has been demonstrated by structure–reactivity studies of electrocatalytic oxidation of small organic molecules. We further observed that Pd nanocrystals exhibited catalytic performance considerably different from bulk Pd single-crystal planes with the same Miller indices. Such differences were attributed to special catalytic functions conferred by nanocrystal edges. This study paves a promising route for investigating catalytic reactions effectively at the atomic level and nanoscales

Ligand-Mediated Electrocatalytic Activity of Pt Nanoparticles for Oxygen Reduction Reactions

High-performance electrocatalysts for oxygen reduction reactions (ORR) are crucial for the development of proton exchange membrane fuel cells (PEMFCs). In this study, a novel method was developed by which the ORR activity of Pt nanoparticles was deliberately manipulated by selective organic capping ligands. By coreduction of diazonium salts and H₂PtCl₄, a series of Pt nanoparticles (core size 2.0–2.5 nm) stabilized by para-substituted (R = −CH₃, −F, −Cl, −OCF₃, and −CF₃) phenyl groups were synthesized. The experimental results demonstrated that the electron-withdrawing capability of the substituent moieties, as manifested by the Hammet substituent constant (σ), plays a key role in controlling the ORR activity, where the higher σ, the higher ORR activity. Within the present experimental context, Pt nanoparticles stabilized by trifluoromethylphenyl groups (Pt–Ar–CF₃) exhibit the highest catalytic activity among the series, with an ORR specific activity 3.2 times higher than that of commercial Pt/C catalysts. The enhanced activity may be correlated with the weakened oxygen adsorption by the electronegative ligands

RhPt Flowerlike Bimetallic Nanocrystals with Tunable Composition as Superior Electrocatalysts for Methanol Oxidation

For the first time, composition-tunable, high-yield, RhPt flowerlike bimetallic nanocrystals were successfully synthesized through an aqueous solution approach. The electrocatalytic activity of these RhPt nanoalloys toward methanol oxidation was investigated and compared to the activity of commercial Pt black and commercial Ru₅₀Pt₅₀/C. The RhPt flowerlike bimetallic nanoallys have shown composition-dependent and superior catalytic properties relative to those of commercial Pt black and commercial Ru₅₀Pt₅₀/C. The peak current density and mass current value of Rh₁₉Pt₈₁ nanoalloys are 0.75 mA cm^–2 and 0.12 mA μg^–1, respectively. For commercial Pt black, they are 0.48 mA cm^–2 and 0.074 mA μg^–1, and for commercial Ru₅₀Pt₅₀/C, they are 0.28 mA cm^–2 and 0.10 mA μg^–1. Moreover, the chronoamperometric measurements show that the RhPt flowerlike nanoalloys have excellent stability over commercial Pt black and commercial Ru₅₀Pt₅₀/C

Low-cost transition metal–nitrogen–carbon electrocatalysts for the oxygen reduction reaction: operating conditions from aqueous electrolytes to fuel cells

After decades of effort, the performance of low-cost transition metal–nitrogen–carbon (M–N–C) catalysts has been significantly improved, positioning them as promising catalysts for the oxygen reduction reaction in proton-exchange-membrane fuel cells (PEMFCs). Despite this progress, compared to traditional commercial Pt/C catalysts, the practical application of M–N–C catalysts in PEMFCs is hindered by their inferior performance in acidic environments. In this perspective, we first summarize the current status of M–N–C catalysts in terms of activity and stability, and compare their performance with that of Pt/C catalysts. Then we discuss the fundamental research challenges associated with M–N–C catalysts, which are primarily related to (i) conducting basic research with tests exclusively using oversimplified aqueous electrolytes that limits exploration in practical fuel cell environments; (ii) lacking operando characterization methods under fuel cell working conditions; and (iii) the complexity of catalyst structures and fuel cell operating environments causing difficulty in M–N–C catalyst research. Lastly, we propose key advances that need to be made in the future to address these fundamental challenges, including the rational design of fit-for-purpose catalysts based on more cost-effective and efficient modelling, preparing model/quasi-model catalysts with defined and controllable structures, and developing operando characterization techniques for PEMFCs. By combined study using model/quasi-model catalysts, operando characterization methods and atomistic modeling, we can deeply understand the “structure-performance” relationship of the catalysts at various scales and develop next generation M–N–C catalysts that can meet the increased demand for PEMFCs.</p

Computing Prediction and Functional Analysis of Prokaryotic Propionylation

Identification and systematic analysis of candidates for protein propionylation are crucial steps for understanding its molecular mechanisms and biological functions. Although several proteome-scale methods have been performed to delineate potential propionylated proteins, the majority of lysine-propionylated substrates and their role in pathological physiology still remain largely unknown. By gathering various databases and literatures, experimental prokaryotic propionylation data were collated to be trained in a support vector machine with various features via a three-step feature selection method. A novel online tool for seeking potential lysine-propionylated sites (PropSeek) (http://bioinfo.ncu.edu.cn/PropSeek.aspx) was built. Independent test results of leave-one-out and <i>n</i>-fold cross-validation were similar to each other, showing that PropSeek is a stable and robust predictor with satisfying performance. Meanwhile, analyses of Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathways, and protein–protein interactions implied a potential role of prokaryotic propionylation in protein synthesis and metabolism

Computing Prediction and Functional Analysis of Prokaryotic Propionylation

Identification and systematic analysis of candidates for protein propionylation are crucial steps for understanding its molecular mechanisms and biological functions. Although several proteome-scale methods have been performed to delineate potential propionylated proteins, the majority of lysine-propionylated substrates and their role in pathological physiology still remain largely unknown. By gathering various databases and literatures, experimental prokaryotic propionylation data were collated to be trained in a support vector machine with various features via a three-step feature selection method. A novel online tool for seeking potential lysine-propionylated sites (PropSeek) (http://bioinfo.ncu.edu.cn/PropSeek.aspx) was built. Independent test results of leave-one-out and <i>n</i>-fold cross-validation were similar to each other, showing that PropSeek is a stable and robust predictor with satisfying performance. Meanwhile, analyses of Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathways, and protein–protein interactions implied a potential role of prokaryotic propionylation in protein synthesis and metabolism

Electrochemically Shape-Controlled Synthesis of Pd Concave-Disdyakis Triacontahedra in Deep Eutectic Solvent

Concave-disdyakis triacontahedral palladium nanocrystals (C-DTH Pd NCs) bound with 120 {631} high-index facets were prepared by electrochemically shape-controlled method in deep eutectic solvent (DES). It has found that both the adsorption of urea derived from EDS and the upper (<i>E</i>_U) and lower (<i>E</i>_L) limit potentials of the square-wave potential applied in the synthesis are contributed synergetically in controlling the shape of Pd NCs. The formation of C-DTH Pd NCs with well-defined shape was achieved by the dynamic interaction between urea adsorption at <i>E</i>_U and growth at <i>E</i>_L. In situ FTIR spectroscopic studies revealed that the urea adsorbates at <i>E</i>_U play a crucial role in shape evolution, especially in the formation of C-DTH Pd NCs. It has demonstrated that the as-synthesized C-DTH Pd NCs enclosed by {631} high-index facets exhibit higher electrocatalytic activity than Pd NCs with other shapes bound by {111} low-index facets (octahedral (OH) and icosahedral (IH)) toward ethanol electrooxidation in alkaline medium

Pyrolyzed Fe–N–C Composite as an Efficient Non-precious Metal Catalyst for Oxygen Reduction Reaction in Acidic Medium

Aimed at developing a highly active and stable non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) in acidic proton-exchange membrane fuel cells (PEMFCs), a novel NPMC was prepared by pyrolyzing a composite of carbon-supported Fe-doped graphitic carbon nitride (Fe–g-C₃N₄@C) above 700 °C. In this paper, the influence of the pyrolysis temperature and Fe content on ORR performance was investigated. Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) studies reveal that, with a half-wave potential of 0.75 V [versus reversible hydrogen electrode (RHE)] and a H₂O₂ yield of 2.6% at 0.4 V, the as-synthesized catalyst heat-treated at 750 °C with a Fe salt/dicyandiamide (DCD) mass ratio of 10% displays the optimal ORR activity and selectivity. Furthermore, the pyrolyzed Fe–N–C composite exhibits superior durability in comparison to that of commercial 20 wt % Pt/C in acidic medium, making it a good candidate for an ORR electrocatalyst in PEMFCs