Pt-Mediated Interface Engineering Boosts the Oxygen Reduction Reaction Performance of Ni Hydroxide-Supported Pd Nanoparticles

Recent Advances on Two-Dimensional Nanomaterials Supported Single-Atom for Hydrogen Evolution Electrocatalysts

Water electrolysis has been recognized as a promising technology that can convert renewable energy into hydrogen for storage and utilization. The superior activity and low cost of catalysis are key factors in promoting the industrialization of water electrolysis. Single-atom catalysts (SACs) have attracted attention due to their ultra-high atomic utilization, clear structure, and highest hydrogen evolution reaction (HER) performance. In addition, the performance and stability of single-atom (SA) substrates are crucial, and various two-dimensional (2D) nanomaterial supports have become promising foundations for SA due to their unique exposed surfaces, diverse elemental compositions, and flexible electronic structures, to drive single atoms to reach performance limits. The SA supported by 2D nanomaterials exhibits various electronic interactions and synergistic effects, all of which need to be comprehensively summarized. This article aims to organize and discuss the progress of 2D nanomaterial single-atom supports in enhancing HER, including common and widely used synthesis methods, advanced characterization techniques, different types of 2D supports, and the correlation between structural hydrogen evolution performance. Finally, the latest understanding of 2D nanomaterial supports was proposed.

Iridium Single Atoms to Nanoparticles: Nurturing the Local Synergy with Cobalt-Oxide Supported Palladium Nanoparticles for Oxygen Reduction Reaction

A ternary catalyst comprising Iridium (Ir) single-atoms (SA)s decorated on the Co-oxide supported palladium (Pd) nanoparticles (denoted as CPI-SA) is developed in this work. The CPI-SA with 1 wt.% of Ir exhibits unprecedented high mass activity (MA) of 7173 and 770 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE in alkaline ORR (0.1 m KOH), outperforming the commercial Johnson Matthey Pt catalyst (J.M.-Pt/C; 20 wt.% Pt) by 107-folds. More importantly, the high structural reliability of the Ir single-atoms endows the CPI-SA with outstanding durability, where it shows progressively increasing MA of 13 342 and 1372 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE up to 69 000 cycles (3 months) in the accelerated degradation test (ADT). Evidence from the in situ partial fluorescence yield X-ray absorption spectroscopy (PFY-XAS) and the electrochemical analysis indicate that the Ir single-atoms and adjacent Pd domains synergistically promote the O2 splitting and subsequent desorption of hydroxide ions (OH-), respectively. Whereas the Co-atoms underneath serve as electron injectors to boost the ORR activity of the Ir single-atoms. Besides, a progressive and sharp drop in the ORR performance is observed when Ir-clusters and Ir nanoparticles are decorated on the Co-oxide-supported Pd nanoparticles.

Construction of Pd-Te Intermetallic Compounds to Achieve Ultrastable Oxygen Reduction Activity

Palladium (Pd)-transition metal alloys have the potential to regulate the intermediate surface adsorption strength in oxygen reduction reactions (ORR), making them a promising substitute for platinum-based catalysts. Nonetheless, prolonged electrochemical cycling can lead to the depletion of transition metals, resulting in structural degradation and poor durability. Herein, the synthesis of alloy catalysts (Pd25%Te75%) containing Pd and the metalloid tellurium (Te) through a one-step reduction method is reported. Characterizations of powder X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy demonstrated both uniform dispersion and strong binding force of elements within the PdTe alloy, along with providing crystallographic details of associated compounds. Based on density functional theory calculations, PdTe had a more negative d-band center than that of pure Pd, which reduces the adsorption capacity between active sites and intermediates in the ORR, and therefore enhances reaction kinetics. The Pd25%Te75% exhibited excellent ORR activity, and its onset and half-wave potentials were ∼0.98 and ∼0.90 V, respectively, at 1600 rpm within the O2-saturated 1.0 M KOH. Significantly, accelerated durability tests achieved exceptional stability, and half-wave potential just decayed by 4 mV after 30000 consecutive cycles. Moreover, this study aims to promote the preparation of Pd and metalloid alloys for other energy conversion applications.

Synthesis of MnOOH and its application in a supporting hexagonal Pd/C catalyst for the oxygen reduction reaction

With the expansion of global energy problems and the deepening of research on oxygen reduction reaction (ORR) in alkaline media, the development of low cost and high electrocatalytic performance catalysts has become a research hotspot. In this study, a hexagonal Pd-C-MnOOH composite catalyst was prepared by using the triblock copolymer P123 as the reducing agent and protective agent, sucrose as the carbon source and self-made MnOOH as the carrier under hydrothermal conditions. When the Pd load is 20% and the C/MnOOH ratio is 1 : 1, the 20% Pd-C-MnOOH-1 : 1 catalyst obtained by the one-step method has the highest ORR activity and stability in the alkaline system. At 1600 rpm, the limiting diffusion current density and half-wave potential of the 20% Pd-C-MnOOH-1 : 1 electrocatalyst are -4.78 mA cm-2 and 0.84 V, respectively, which are better than those of the commercial 20%Pd/C catalyst. According to the Koutecky-Levich (K-L) equation and the linear fitting results, the electron transfer number of the 20%Pd-C-MnOOH-1 : 1 electrocatalyst for the oxygen reduction reaction is 3.8, which is similar to that of a 4-electron process. After 1000 cycles, the limiting diffusion current density of the 20%Pd-C-MnOOH-1 : 1 catalyst is -4.61 mA cm-2, which only decreases by 3.7%, indicating that the 20%Pd-C-MnOOH-1 : 1 catalyst has good stability. The reason for the improvement of the ORR performance of the Pd-C-MnOOH composite catalyst is the improvement of the conductivity of the carbon layer formed by original carbonization, the regular hexagonal highly active Pd particles and the synergistic catalytic effect between Pd and MnOOH. The method of introducing triblock copolymers in the synthesis of oxides and metal-oxide composite catalysts is expected to be extended to other electrocatalysis fields.

Rational design of electrocatalytic system to selective transform nitrate to nitrogen

Nitrate (NO3-) is one of the most common pollutants in natural bodies of water and as such threatens both human health and the safety of aquatic environment. There are efficient electrochemical techniques to directly remove NO3-, but inexpensive, selective and electrocatalytic strategies to eliminate NO3- by converting it into benign nitrogen (N2) remain challenging. This work studied Cu particles that were formed directly on a Ni foam (Cu-NF) and evaluated their electrocatalytic NO3- reduction performance. The use of carbon nanotubes (CNT) functionalized with titanium suboxides (TiSO) as the anode facilitated the generation of active chlorine species that had a key role in the removal of NH4+. An electrochemical system that integrated a Cu-NF cathode with a TiSO-CNT anode could remove 88.5% of NO3- with a >99% N2 selectivity when operated over 6 h (4.1 × 10-4 h-1) at a potential of -1.2 V vs Ag/AgCl. Because the chloride ions are very common in natural sources of water, this technique offers a sustainable and environmentally friendly approach for the removal of NO3- from contaminated water sources.

Sub-Millisecond Laser-Irradiation-Mediated Surface Restructure Boosts the CO Production Yield of Cobalt Oxide Supported Pd Nanoparticles

The catalytic conversion of CO₂ into valuable commodities has the potential to balance ongoing energy and environmental issues. To this end, the reverse water-gas shift (RWGS) reaction is a key process that converts CO₂ into CO for various industrial processes. However, the competitive CO₂ methanation reaction severely limits the CO production yield; therefore, a highly CO-selective catalyst is needed. To address this issue, we have developed a bimetallic nanocatalyst comprising Pd nanoparticles on the cobalt oxide support (denoted as CoPd) via a wet chemical reduction method. Furthermore, the as-prepared CoPd nanocatalyst was exposed to sub-millisecond laser irradiation with per-pulse energies of 1 mJ (denoted as CoPd-1) and 10 mJ (denoted as CoPd-10) for a fixed duration of 10 s to optimize the catalytic activity and selectivity. For the optimum case, the CoPd-10 nanocatalyst exhibited the highest CO production yield of ∼1667 μmol g^-1_catalyst, with a CO selectivity of ∼88% at a temperature of 573 K, which is a 41% improvement over pristine CoPd (~976 μmol g^-1_catalyst). The in-depth analysis of structural characterizations along with gas chromatography (GC) and electrochemical analysis suggested that such a high catalytic activity and selectivity of the CoPd-10 nanocatalyst originated from the sub-millisecond laser-irradiation-assisted facile surface restructure of cobalt oxide supported Pd nanoparticles, where atomic CoOx species were observed in the defect sites of the Pd nanoparticles. Such an atomic manipulation led to the formation of heteroatomic reaction sites, where atomic CoOx species and adjacent Pd domains, respectively, promoted the CO₂ activation and H₂ splitting steps. In addition, the cobalt oxide support helped to donate electrons to Pd, thereby enhancing its ability of H₂ splitting. These results provide a strong foundation to use sub-millisecond laser irradiation for catalytic applications.

LiNi0.6Co0.2Mn0.2O2 Cathode-Solid Electrolyte Interfacial Behavior Characterization Using Novel Method Adopting Microcavity Electrode

Due to the limitations of organic liquid electrolytes, current development is towards high performance all-solid-state lithium batteries (ASSLBs). For high performance ASSLBs, the most crucial is the high ion-conducting solid electrolyte (SE), with a focus on interface analysis between SE and active materials. In the current study, we successfully synthesized the high ion-conductive argyrodite-type (Li₆PS₅Cl) solid electrolyte, which has 4.8 mS cm^-1 conductivity at room temperature. Additionally, the present study suggests the quantitative analysis of interfaces in ASSLBs. The measured initial discharge capacity of a single particle confined in a microcavity electrode was 1.05 nAh for LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)-Li₆PS₅Cl solid electrolyte materials. The initial cycle result shows the irreversible nature of active material due to the formation of the solid electrolyte interphase (SEI) layer on the surface of the active particle; further second and third cycles demonstrate high reversibility and good stability. Furthermore, the electrochemical kinetic parameters were calculated through the Tafel plot analysis. From the Tafel plot, it is seen that asymmetry increases gradually at high discharge currents and depths, which rise asymmetricity due to the increasing of the conduction barrier. However, the electrochemical parameters confirm the increasing conduction barrier with increased charge transfer resistance.