Origins of Less Noble Behavior by Au during CO Adsorption

An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au

In the most recent decade, glycerol electrooxidation (GEOR) has attracted extensive research interest for valorization of glycerol: the conversion of glycerol to value-added products. These reactions at platinum, palladium, and gold electrodes have a lot of uncertainty in their reaction mechanisms, which has generated some controversies. This review gathers many reported experimental results, observations and proposed reaction mechanisms in order to draw a full picture of GEOR. A particular focus is the clarification of two propositions: Pd is inferior to Pt in cleaving the C-C bonds of glycerol during the electrooxidation and the massive production of CO₂ at high overpotentials is due to the oxidation of the already-oxidized carboxylate products. It is concluded that the inferior C-C bond cleavability with Pd electrodes, as compared with Pt electrodes, is due to the inefficiency of deprotonation, and the massive generation of CO₂ as well as other C1/C2 side products is partially caused by the consumption of OH^- at the anodes, as a lower pH reduces the amount of carboxylates and favors the C-C bond scission. A reaction mechanism is proposed in this review, in which the generation of side products are directly from glycerol ("competition" between each side product) rather than from the further oxidation of C2/C3 products. Additionally, GEOR results and associated interpretations for Ni electrodes are presented, as well as a brief review on the performances of multi-metallic electrocatalysts (most of which are nanocatalysts) as an introduction to these future research hotpots.

On-Chip Electrical Transport Investigation of Metal Nanoparticles: Characteristic Acidic and Alkaline Adsorptions Revealed on Pt and Au Surface

Metal nanocrystals have been extensively explored as efficient and tailorable electrocatalysts for various sustainable energy technologies. Precise understanding of molecular interactions at the electrode-electrolyte interfaces during electrochemical processes, which mostly relies on the interpretation of spectroscopic surface information, is crucial to the innovations in catalyst design and optimization of reaction conditions. Here, we demonstrate the first in situ electrical transport evidence of pH-dependent surface anionic adsorptions on metal nanoparticles (MNPs), enabled by the on-chip electrical transport spectroscopy (ETS) of continuous nanoparticle (NP) thin films. Our results on platinum and gold NPs reveal the significant (and distinct) impacts of acid-base environments on their surface adsorption features, which contributes to the further understanding of gold- and platinum-based electrocatalytic systems. The successful employment of ETS on metal nanoparticles achieves a more general transport-based signaling technique that conveniently fits the abundance of catalytic materials with zero-dimension morphology.

Revealing Energetics of Surface Oxygen Redox from Kinetic Fingerprint in Oxygen Electrocatalysis

The key step for rational catalyst design in heterogeneous electrocatalysis is to reveal the distinctive energy profile of redox reactions of a catalyst that give rise to specific activity. However, it is challenging to experimentally obtain the energetics of oxygen redox in oxygen electrocatalysis because of the liquid reaction environment. Here we develop a kinetic model that constructs a quantitative relation between the energy profile of oxygen redox and electrochemical kinetic fingerprints. The detailed study here demonstrates that the kinetic fingerprints observed from experiments can be well described by different energetics of oxygen redox. On the basis of the model, a feasible methodology is demonstrated to derive binding energies of the oxygen intermediates from electrochemical data. The surface property of different catalysts derived from our model well rationalizes the experimental trends and predicts potential directions for catalyst design.

Octahedral gold-silver nanoframes with rich crystalline defects for efficient methanol oxidation manifesting a CO-promoting effect

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au₃Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au₃Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm⁻², 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au₃Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH⁻ co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

Direct methanol fuel cells are promising for clean, sustainable energy, but catalysts should be optimized. Here the authors construct ultrathin nanoframes with rich crystalline defects to increase electrocatalytic activity of gold for methanol oxidation, which is surprisingly promoted by carbon monoxide.