Cu and Pd nanoparticles supported on a graphitic carbon material as bifunctional HER/ORR electrocatalysts

Ultrasonic treatment-assisted reductive deposition of Cu and Pd nanoparticles on ultrathin 2D Bi2S3 nanosheets for selective electrochemical reduction of CO2 into C2 compounds

In this work, we have ultrasonically deposited Cu and Pd nanoparticles on Bi2S3 nanoparticles, prepared using an ultrasonication assisted hydrothermal method. We implemented intense ultrasonic waves bearing frequency of 20 kHz and power of 750 W at the acoustic wavelength of 100 mm to reduce Cu and Pd nanoparticles on the Bi2S3 surface. The XRD confirmed the formation of highly crystalline Bi2S3 nanoparticles with a pure orthorhombic phase and the deposition of copper (Cuo) and palladium (Pdo) nanoparticles was indicated by the strengthening and broadening of the peaks. XPS also confirmed the formation of Cuo and Pdo nanoparticles on Bi2S3. The Transmission Electron Microscopy (TEM) also exhibited the deposition of Cu and Pd nanoparticles on the Bi2S3 nanosheets which was further confirmed using high resolution TEM analysis. The electrochemical CO2 reduction by Cu-Pd/Bi2S3 electrocatalyst using Cu foam as the conducting support led to the formation of acetaldehyde and ethylene as the major products. The rate of formation of ethylene was found to be 488.5 μ mol g-1h-1 at an applied potential of -0.6 V (vs. RHE), with the best Faradaic efficiency of 57.09 % at -0.4 V (vs. RHE). Among the liquid phase products, acetaldehyde was the major product showing the maximum Faradaic efficiency of 6.473 % at -0.2 V (vs. RHE), with a total formation rate of 64.27 μ mol g-1h-1. The results revealed that the Cu-Pd/Bi2S3 electrocatalyst was more selective to C2 products while the pure Bi2S3 nanoparticles majorly produced C1 compounds.

Electronic-Structure-Modulated Cu,Co-Coanchored N-Doped Nanocarbon as a Difunctional Electrocatalyst for Hydrogen Evolution and Oxygen Reduction Reactions

To alleviate the problems of environmental pollution and energy crisis, aggressive development of clean and alternative energy technologies, in particular, water splitting, metal-air batteries, and fuel cells involving two key half reactions comprising hydrogen evolution reaction (HER) and oxygen reduction (ORR), is crucial. In this work, an innovative hybrid comprising heterogeneous Cu/Co bimetallic nanoparticles homogeneously dispersed on a nitrogen-doped carbon layer (Cu/Co/NC) was constructed as a bifunctional electrocatalyst toward HER and ORR via a hydrothermal reaction along with post-solid-phase sintering technique. Thanks to the interfacial coupling and electronic synergism between the Cu and Co bimetallic nanoparticles, the Cu/Co/NC catalyst showed improved catalytic ORR activity with a half-wave potential of 0.865 V and an excellent stability of more than 30 h, even compared to 20 wt% Pt/C. The Cu/Co/NC catalyst also exhibited excellent HER catalytic performance with an overpotential of below 149 mV at 10 mA/cm2 and long-term operation for over 30 h.

Ternary (molybdenum disulfide/graphene)/carbon nanotube nanocomposites assembled via a facile colloidal electrostatic path as electrocatalysts for the oxygen reduction reaction: Composition and nitrogen-doping play a key role in their performance

Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS2/GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure-activity relationships. Both the (MoS2/GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N-GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS2/N-GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further.

Exploring the synergistic effect of palladium nanoparticles and highly dispersed transition metals on carbon nitride/super-activated carbon composites for boosting electrocatalytic activity

In the present work, multifunctional electrocatalysts formed by palladium nanoparticles (Pd NPs) loaded on Fe or Cu-containing composite supports, based on carbon nitride (C3N4) and super-activated carbon with a high porosity development (SBET 3180 m2/g, VDR 1.57 cm3/g, and VT 1.65 cm3/g), were synthesised. The presence of Fe or Cu sites favoured the formation of Pd NPs with small average particle size and a very narrow size distribution, which agreed with Density Functional Theory (DFT) calculations showing that the interaction of Pd clusters with C3N4 flakes is weaker than with Cu- or Fe-C3N4 sites. The electroactivity was also dependent on the composition and, as suggested by preliminary DFT calculations, the Pd-Cu catalyst showed lower overpotential for hydrogen evolution reaction (HER) while bifunctional oxygen reduction reaction/ oxygen evolution reaction (ORR/OER) behaviour was superior in Pd-Fe sample. The Pd-Fe electrocatalyst was studied in a zinc-air battery (ZAB) for 10 h, showing a performance similar to a commercial Pt/C + RuO2 catalyst with a high content of precious metal. This study demonstrates the synergistic effect between Pd species and transition metals and shows that transition metals anchored on C3N4-based composite materials promote the electroactivity of Pd NPs in HER, ORR and OER due to the interaction between both species.

Synthesis of a carbon-wrapped microsphere MoO2/Mo2C heterojunction as an efficient electrocatalyst for the oxygen reduction reaction and the hydrogen evolution reaction

The development of non-noble metal catalysts for the optimization of conversion and storage devices is an important research topic. Hence, the microsphere MoO2/Mo2C/C heterojunction composites, which play an important role in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER), were synthesized using the solvothermal-sintering method. The results revealed that the as-prepared composite exhibited better ORR and HER catalytic performances than those of MoO2/Mo2C and Vulcan XC-72R (carbon black), and approaching that of commercial Pt/C. At the same time, it has a superior methanol tolerance and electrochemical stability than that of the commercial Pt/C. The excellent performance may be attributed to the synergistic effect of the MoO2/Mo2C heterostructure, highly conductive Vulcan XC-72R, and oxygen vacancies (Ov). This research offers new insights into the design and synthesis of cost-effective, environmentally friendly heterojunction composite catalysts used as a high-performance cathode material in fuel cells and water splitting.

Electrocatalytic Oxygen Reduction Reaction by the Pd/Fe-N-C Catalyst and Application in a Zn–Air Battery

Developing a non-platinum catalyst that effectively catalyzes the oxygen reduction reaction (ORR) is highly significant for metal–air batteries. Metal and nitrogen co-doped carbons (M-N-Cs) have emerged as alternative candidates to platinum. In this work, dual-metal Pd/Fe-N-C electrocatalysts were synthesized by the one-step pyrolysis of phytic acid, melamine, and Pd/Fe-based salts. The Pd/Fe-N-C catalyst exhibited a good catalytic ability during the ORR process and outperformed the commercial Pt/C catalyst as regards mass activity, catalytic stability, and methanol tolerance. It was found that Pd-Nx is the active center, and the synergistic effect from the Fe component introduction endowed the Pd/Fe-N-C with an excellent catalytic performance towards the ORR. When assembled into a Zn–air battery, its specific capacity was ~775 mAh gZn−1. Meanwhile, the peak power density could reach 3.85 W mgPd−1, i.e., 3.4 times that of the commercial Pt/C catalyst (1.13 W mgPt−1). This implies that the Pd/Fe-N-C catalyst has potential applications in metal–air batteries.

Solution combustion synthesis of ternary Ni/WC/C composites with efficient electrocatalytic oxygen reduction performance

In this paper, a fast processing route involving a wet-chemical method (solution combustion synthesis, SCS) and carbonization in a CH₄ environment was demonstrated, through which nanosized Ni/WC/C powder with an average size of 80 nm was obtained. In the catalyst powder, Ni was evenly distributed and it could form NiOOH to promote catalysis, and an amorphous carbon (C) layer with a thickness of <10 nm was formed on the surface of the composite particles, improving the stability of the Ni/WC powder and promoting electron transport. Due to the characteristics of uniformity and a large specific surface area and the synergistic effect of Ni, WC, and C, this powder showed significantly improved ORR catalytic activity in alkaline solution. When the amount of Ni doping was 15 wt%, the composite powder showed the smallest particle size and the best ORR catalytic performance. Its cathode peak potential was -0.31 V and the half wave potential was -0.34 V. The number of electrons transferred in the ORR reaction was 3.6. This work provided a fast and cheap method for the preparation of multicomponent composite catalyst materials.