ORR activity and electrochemical stability for well-defined topmost and interface structures of the Pt/Pd(111) bimetallic system

Progress in Experimental Methods Using Model Electrodes for the Development of Noble-Metal-Based Oxygen Electrocatalysts in Fuel Cells and Water Electrolyzers

Hydrogen plays a key role in maximizing the benefits of renewable energy, and the widespread adoption of water electrolyzers and fuel cells, which convert the chemical energy of hydrogen and electrical energy into each other, is strongly desired. Electrocatalysts used in these devices, typically in the form of nanoparticles, are crucial components because they significantly affect cell performance, but their raw materials rely on limited resources. In catalyst research, electrochemical experimental studies using model catalysts, such as single-crystal electrodes, have provided valuable information on reaction and degradation mechanisms, as well as catalyst development strategies aimed at overcoming the trade-off between activity and durability, across spatial scales ranging from the atomic to the nanoscale. Traditionally, these experiments are conducted using well-defined, simple model surfaces like bare single-crystal electrodes in pure systems. However, in recent years, experimental methods using more complex interfaces-while still precisely controlling elemental distribution, microstructure, and modification patterns-have been established. This paper reviews the history of those studies focusing on noble-metal-based electrocatalysts for oxygen reduction reactions and oxygen evolution reactions, which account for the majority of efficiency losses in fuel cells and water electrolyzers, respectively. Furthermore, potential future research themes in experimental studies using model electrodes are identified.

Theoretical study of Mo2N supported transition metal single-atom catalyst for OER/ORR bifunctional electrocatalysis

The rational design and development of an efficient bifunctional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the key to developing new renewable energy storage and conversion technologies. Transition metal nitrides (TMNs) have shown excellent energy storage and electrochemistry potential due to their unique electronic structure and physicochemical properties. In this paper, based on the first-principles method of density functional theory (DFT), a series of efficient and stable bifunctional single-atom catalysts (SACs) were designed on Mo2N by introducing transition metal atoms as active sites, and the effects of different TM atoms on the catalytic performance of 2D-Mo2N (Two dimensional Mo2N) were evaluated. The calculation results show that TM@Mo2N exhibits excellent stability and good conductivity, which is conducive to electron transfer during the electrocatalytic reaction. Among these SACs, the Au@Mo2N single-atom catalyst has a very low OER overpotential (0.36 V), exhibiting high OER activity. Meanwhile, Au@Mo2N also exhibits excellent ORR performance with a low overpotential of 0.4 V, indicating that Au@Mo2N is the best OER/ORR bifunctional catalyst. This work provides a feasible solution for developing transition metal bifunctional electrocatalysts. Au@Mo2N is expected to replace traditional commercial Pt catalyst materials and become a catalyst with excellent performance in fuel cell modules.

First-principles study of the effect of compressive strain on oxygen adsorption in Pd/Ni/Cu-alloy-core@Pd/Ir-alloy-shell catalysts

Through synergism between the ligand effect, the d-band center shift, and the surface alloying effect, the Pd₃CuNi@PdIr catalyst exhibits the poorest dioxygen adsorption and, consequently, the best catalytic ORR performance.

Alloy-composition-dependent oxygen reduction reaction activity and electrochemical stability of Pt-based bimetallic systems: a model electrocatalyst study of Pt/PtxNi100-x(111)

The oxygen reduction reaction (ORR) activity and electrochemical stability of well-defined n monolayer (ML)-Pt/Pt_xNi_100-x(111) (n = 2 and 4; x = 75, 50, and 25) model electrocatalyst surfaces were investigated in this study. The initial activity of the as-prepared two-monolayered Pt-covered Pt_xNi_100-x(111) substrates (2ML-Pt/Pt_xNi_100-x(111)) increased with increasing Ni composition in the Pt_xNi_100-x(111) substrate. In particular, 2ML-Pt/Pt₂₅Ni₇₅(111) showed the initial activity that was 25 times higher than that of clean Pt(111) although the higher Ni composition resulted in destabilization of the catalyst upon the application of potential cycles (PCs). As for 4ML-Pt/Pt_xNi_100-x(111), activity enhancements were insensitive to alloy composition and thicker Pt shell layers stabilized the catalyst against PC applications. In particular, the activities of 4ML-Pt/Pt₅₀Ni₅₀(111) and 4ML-Pt/Pt₂₅Ni₇₅(111) gradually increased during 1000 PCs probably because of the PC-induced mono-atomic heights and nanometer-size islands that had (110) and (100) steps introduced into the topmost (111) terraces. Thus, the simultaneous tuning of core-alloy composition and Pt shell thickness is vital for developing practical, highly efficient Pt-based alloy ORR electrocatalysts.