Electronic Structure Effect of PtCo Alloy with Adjustable Compositions for Efficient Methanol Electrooxidation.

Various efficient strategies have been developed to overcome the anodic electrocatalyst issue of methanol-based fuel cells owing to their complicated methanol electrooxidation mechanism. In this work, PtCo nanoparticles with adjustable compositions supported on multiwalled carbon nanotubes (Pt1Cox/MWCNTs) through the adsorbing-coating-annealing-etching route were synthesized. Compared with the Pt/C catalyst, Pt1Co3/MWCNTs exhibit better electrocatalytic MOR activity in both activity and durability. Notably, the electrochemical mass and specific activity of the as-prepared catalyst are 1.04 mA µg-1Pt and 2.18 mA cm-2, respectively, which are higher than those of the Pt/C catalyst. Moreover, the as-prepared sample revealed lower onset potential during the CO stripping test. Furthermore, the Pt1Co3/MWCNTs possess a lower current density decrease rate in chronoamperometry and cyclic durability tests. The enhancement of activity and stability of Pt1Co3/MWCNTs could be ascribed to their ordered morphological structure, the electronic interaction between MWCNTs and PtCo nanoparticles, and the suitable electronic structure effect between Pt/Co ratios. The concept of the catalyst design in this study offers a different guideline for constructing the novel methanol electrooxidation catalyst, which will accelerate the widespread fuel cell practical application.

Intrinsic effects of strain on low-index surfaces of platinum: roles of the five 5d orbitals.

Surface strain has been widely applied in catalyst design. It has been reported that tensile strain can weaken the adsorption of species on certain metal surfaces similar to the effects of compressive strain. This result contradicts the widely accepted rule predicated on the d-band center. Here, by using DFT calculations, we confirmed the abnormal adsorption behaviour of certain species on strained Pt low-index surfaces and found that the behaviour is dependent on the surfaces and species. Tensile strain on the close-packed Pt(111) and Pt(100) surfaces enhances species adsorption, while tensile strain on the open Pt(110) surface weakens species adsorption. This result is attributed to the asynchronous change in the five 5d orbitals due to the inconsistency between interlayer contraction and biaxial stretching. The dramatic contraction of interlayer spacing on the tensile strained Pt(110) surface sharply downshifts the dz2 center, then weakens species adsorption. Thus, due to the different roles of the five d orbitals in binding species, the inconsistent change in the five d orbitals is the intrinsic mechanism of the effects of strain on metal catalysts. Selectively tuning the five d orbitals might provide a new strategy to modify the adsorption behaviour of species on Pt-based catalysts and may result in extraordinarily high catalytic activities.

Accelerated alkaline hydrogen evolution on M(OH) x /M-MoPO x (M = Ni, Co, Fe, Mn) electrocatalysts by coupling water dissociation and hydrogen ad-desorption steps.

Developing efficient and cheap electrocatalysts for the alkaline hydrogen evolution reaction is still a big challenge due to the sluggish water dissociation kinetics as well as poor M-Had energetics. Herein, hydroxide modification and element incorporation have been demonstrated to realize a synergistic modulation on a new class of M(OH) x /M-MoPO x catalysts for accelerating water dissociation and hydrogen ad-desorption steps in the HER. Theoretical and experimental results disclosed that in situ modification with hydroxide endowed M(OH) x /M-MoPO x with a strong ability to dissociate water, and meanwhile, oxygen incorporation effectively optimized the M-Had energetics of the NiMoP catalyst. Moreover, the interaction between M(OH) x and M-MoPO x components in M(OH) x /M-MoPO x further enhances their ability to catalyze the two elementary steps in alkaline hydrogen evolution, providing a wide avenue for efficiently catalyzing hydrogen evolution. In general, the optimized Ni(OH)2/NiMoPO x catalyst exhibits excellent alkaline HER activity and durability, superior to the state-of-the-art Pt/C catalyst when the overpotential exceeds 65 mV.

Role of non-metallic atoms in enhancing the catalytic activity of nickel-based compounds for hydrogen evolution reaction.

The transition-metal compounds (MX) have gained wide attention as hydrogen evolution reaction (HER) electrocatalysts; however, the interaction between the non-metallic atom (X) and the metal atom (M) in MX, and the role of X in the enhanced catalytic activity of MX, are still ambiguous. In this work, we constructed a simple model [X/Ni(100)] to decipher the contribution of X towards enhancing the catalytic activity of NiX, which allows us to accurately predict the trend in HER catalytic activity of NiX based on the easily accessible physico-chemical characteristics of X. Theoretical calculations showed that the electronegativity (χX) and the principle quantum number (nX) of X are two important descriptors for evaluating and predicting the HER catalytic activity of NiX catalysts effectively. X atoms in the VIA group can enhance the HER activity of X/Ni(100) more significantly than those in the second period due to the large χX or nX. At a relatively low X coverage, the S/Ni(100) possesses the best HER activity among all of the discussed X/Ni(100) models, and the optimum surface S : Ni atomic ratio is about 22-33%. Further experiments demonstrated that the Ni-Ni3S2 catalyst with a surface S : Ni atomic ratio of 28.9% exhibits the best catalytic activity and lowest charge transfer resistance. The trend in catalytic activity of NiX with differing X offers a new possible strategy to exploit MX materials and design new active catalysts rationally.