Perspective

Recent progress on oxygen and hydrogen peroxide reduction reactions on Pt single crystal electrodes

Transition metal oxides have shown potential as hydrogen peroxide (H₂O₂) reduction catalysts because of their low cost, good catalytic properties, and excellent stability in alkaline solutions. In this study, a CNF-0.25 composite electrode comprising spider chrysanthemum-like Co flowers on a Ni foam is synthesized as an efficient cathode for H₂O₂ electroreduction in alkaline media. CNF-0.25 exhibited superior stability and highly desirable electrocatalytic properties for H₂O₂ reduction with a high current density of 0.42 A cm⁻² at − 0.5 V. The voltage of an Al-H₂O₂ semi-fuel cell prepared using CNF-0.25 as the cathode remains stable during a 50 h discharge test. The specific mechanism for the promotion of H₂O₂ electroreduction using CNF-0.25 is investigated according to the mechanism of H₂O₂ reduction over a cobalt-based catalyst. The spider chrysanthemum-like Co flowers are mainly composed of metallic Co, which improves the conductivity of the electrode. On the surface of the metallic Co, the presence of a layer of cobalt oxides or hydroxides provides sufficient catalytic active sites (Co²⁺/Co³⁺) and prevents further oxidation of internal Co. In addition, the unique spider chrysanthemum-like structure of CNF-0.25 increases the specific surface area of the electrode and facilitates electrolyte transport. This work offers another approach for designing highly efficient transition metal oxide electrodes in alkaline media.

Fuel cells have attracted extensive attention due to their high conversion efficiency and environmental friendliness. However, their wider application is limited by the poor activity and high cost of platinum (Pt), which is widely used as the cathode catalyst to overcome the slow kinetics associated with oxygen reduction reaction (ORR). Pt-based composites with one-dimensional (1D) nanoarchitectures demonstrate great advantages towards efficient ORR catalysis. This review focuses on the recent advancements in the design and synthesis of 1D Pt-based ORR catalysts. After introducing the fundamental ORR mechanism and the advanced 1D architectures, their synthesis strategies (template-based and template-free methods) are discoursed. Subsequently, their morphology and structure optimization are highlighted, followed by the superstructure assembly using 1D Pt-based blocks. Finally, the challenges and perspectives on the synthesis innovation, structure design, physical characterization, and theoretical investigations are proposed for 1D Pt-based ORR nanocatalysts. We anticipate this study will inspire more research endeavors on efficient ORR nanocatalysts in fuel cell application.

Platinum-based ultrathin core–shell nanosheets catalyst with moderate shell thickness have great potential to solve the problems of highly active catalyst for oxygen reduction reaction (ORR) within proton exchange membrane fuel cells (PEMFCs). Herein, three kinds of Pd/PtNi core–shell nanosheets (Pd@PtNi NSs) catalyst under different shell thickness were developed by a synthetic strategy of depositing platinum-nickel (Pt-Ni) precursors on palladium nanosheets (Pd NSs). The ORR electrocatalytic performance of Pd@PtNi NSs–1, Pd@PtNi NSs–2 and Pd@PtNi NSs–3 catalysts were investigated using commercial Pt/C catalyst for comparison reasons. It is found that the Pd@PtNi NSs–2 catalyst with moderate shell thickness showed excellent ORR performance. Under 0.9 V (vs. reversible hydrogen electrode (RHE)), Pd@PtNi NSs–2 (1.038 A mg^-1_Pt+Pd) achieved mass activity (MA) 6.25 times of commercial Pt/C catalyst. Superior performance of Pd@PtNi NSs–2 was mainly attributed to: i) the ultrathin layer structure, ii) the core–shell structure, iii) the maximum coverage of Pd core, and iv) the maximum surface alloying by surface atomic diffusion.

In this work, highly monodispersed Pt-Ni alloy nanoparticles were directly deposited on carbon substrate through a facile electrodeposition strategy in the solvent system of N,N-dimethylformamide (DMF). A series of carbon supported Pt-Ni alloy electrocatalysts were synthesized under different applied electrode potentials. Among all as-obtained samples, the Pt-Ni/C electrocatalyst deposited at –1.73 V exhibits the optimal specific activity up to 1.850 mA cm⁻² at 0.9 V vs. RHE, which is 6.85 times higher than that of the commercial Pt/C. Comprehensive physiochemical characterizations and computational evaluations via density functional theory were conducted to unveil the nucleation and growth mechanism of PtNi alloy formation. Compared to the aqueous solution, DMF solvent molecule must not be neglected in avoiding particle agglomeration and synthesis of monodispersed nanoparticles. During the alloy co-deposition process, Ni sites produced through the reduction of Ni(II) precursor not only facilitates Pt-Ni alloy crystal nucleation but also in favor of further Pt reduction on the Ni-inserted Pt surface. As for the deposition potential, it adjusts the final particle size. This work provides a hopeful extended Pt-based catalyst layer production strategy for proton exchange membrane fuel cells and a new idea for the nucleation and growth mechanism exploration for electrodeposited Pt alloy.

Most of the previous studies have investigated the detonation and combustion characteristics of hydrogen and air mixtures, but the change process of hydrogen-air recombination reaction at ambient temperature is unclear. In this study, the variation of temperature and hydrogen conversion during the H₂-air mixture reaction catalyzed by Pt/C catalyst was examined. Experiments were carried out in a small-scale cylindrical vessel to investigate the effects of hydrogen volume fraction, catalyst mass, and inlet gas flow rate on the reaction process. The results revealed that the reaction temperature climbed as the hydrogen volume fraction increased, with a peak value achieved when the hydrogen volume fraction reached 35 vol%, and subsequently reduced as the hydrogen volume fraction increased further. The increase of the inlet gas flow rate also promoted the growth of reaction temperature. However, there was no significant linear relationship between the rise of catalyst mass and the change of reaction temperature.