Downshift Of D-band Center Research Articles

Radical to non-radical conversion during PMS activation triggered by optimized electronic structure: Orientational regulation of oxidation pathway for water remediation

The orientational regulation of non-radical pathways is significant in the peroxymonosulfate (PMS)-based AOP for practical potential, but remains challenge. Here, the Se-doped Co(OH)2 hollow spheres (CoHS-Se-CR) were designed for PMS activation to rapidly degrade gatifloxacin (GAT) antibiotic, with over 95 % GAT removal in 20 min. DFT and experimental trials reveal the downshift of d-band center of Co 3d and O − H bond stretch in PMS via Se doping of Co(OH)2. The active HSO5•− generated via the breaking of O–H bond triggers the radical to the non-radical conversion of the degradation mechanism, dominated by 1O2 and assisted by electron transport process. Both oxygen vacancy and Se(Ⅵ) were involved in 1O2 generation and Co(III)/Co(II) cycle. The CoHS-Se-CR/PMS system showed high efficiency for GAT removal in a wide pH range and strong resistance to anionic interference. This work provides a new strategy for designing PMS activators to construct orientational non-radical AOP.

Engineering Interfacial Pt─O─Ti Site at Atomic Step Defect for Efficient Hydrogen Evolution Catalysis.

The hydrogen evolution reaction (HER) activity of defect-stabilized low-Pt-loading catalysts is closely related with defect type in support materials, while the knowledge about the effect of higher-dimensional defects on the property and activity of trapped Pt atomic species is scarce. Herein, small size (5-10nm) TiO2 nanoparticles with abundant surface step defects (one kind of line defect) are used to direct the uniform anchoring of Pt atomic clusters (Pt-ACs) via Pt─O─Ti linkage. The as-made low-Pt catalysts (Pt-ACs/S-TiO2-NP) exhibit exceptional HER intrinsic activity due to the unique step-site Pi-O-Ti species, in which the mass activity and turnover frequency are as high as 21.46AmgPt -1 and 21.69s-1 at the overpotential of 50mV, both far beyond those of benchmark Pt/C catalysts and other Pt-ACs/TiO2 samples with less step sites. Spectroscopic measurements and theoretical calculations reveal that the step-defect-located Pt─O─Ti sites can simultaneously induce the charge transfer from TiO2 substrate to the trapped Pt-ACs and the downshift of d-band center, which helps the proton reduction to H* intermediates and the following hydrogen desorption process, thus improving the HER. The work provides a deep insight on the interactions between high-dimensional defect and well-dispersed atomic metal motifs for superior HER catalysis.

PtZn alloy nanoparticles with enhanced activity and stability synthesized by a simplified polyol process for electro-oxidation of ammonia

This work reports the synthesis of bimetallic alloy PtZn nanoparticles (NPs) using one-pot glycerol-assisted polyol technique in the presence of Pt(acac)2 and Zn(acac)2 for the electrocatalysis of ammonia fuels. Three different compositions of PtnZn/C (n = 1, 2, 3) electrocatalysts are synthesized in which Pt-content is varied with a fixed Zn-content. PtZn NPs are characterized by X-ray diffractometry (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) for their crystal structures, elemental compositions, and morphological studies. The high-angle annular dark field-scanning TEM-EDS elemental mapping has confirmed that NPs are alloyed with Pt and Zn elements. The electronic structures of alloy NPs are further analyzed by X-ray photoelectron spectroscopy and found a ligand effect resulting in the downshift of d-band center. The incorporation of Zn in NPs decreases the oxygenated species on Pt surface proven by cyclic voltammetry. PtZn NPs are employed for the electrocatalysis of ammonia fuels, namely NH4OH, NH4Cl, NH4NO3, and (NH4)2SO4, where PtZn/C system has shown better electrocatalytic activity than Pt/C. Stability tests are conducted using chronoamperometry for all electrocatalysts of which PtZn/C electrocatalysts have been observed to have good sustainability in the electrochemical environment compared to Pt/C.

Precise synthetic control of exclusive ligand effect boosts oxygen reduction catalysis

Ligand effect, induced by charge transfer between catalytic surface and substrate in core/shell structure, was widely proved to benefit Pt-catalyzed oxygen reduction reaction by tuning the position of d-band center of Pt theoretically. However, ligand effect is always convoluted by strain effect in real core/shell nanostructure; therefore, it remains experimentally unknown whether and how much the ligand effect solely contributes electrocatalytic activity improvements. Herein, we report precise synthesis of a kind of Pd3Ru1/Pt core/shell nanoplates with exclusive ligand effect for oxygen reduction reaction. Layer-by-layer growth of Pt overlayers onto Pd3Ru1 nanoplates can guarantee no lattice mismatch between core and shell because the well-designed Pd3Ru1 has the same lattice parameters as Pt. Electron transfer, due to the exclusive ligand effect, from Pd3Ru1 to Pt leads to a downshift of d-band center of Pt. The optimal Pd3Ru1/Pt1-2L nanoplates achieve excellent activity and stability for oxygen reduction reaction in alkaline/acid electrolyte.

High stability copper clusters anchored on N-doped carbon nanosheets for efficient CO2 electroreduction to HCOOH

Cu-based nanomaterials is crucial for electrochemical CO2 reduction reaction (CO2RR), but they inevitably undergo performance degradation due to structural self-reconstruction at a large current density during CO2RR. Here, we developed a pre-synthetic atomically dispersed Cu source strategy to fabricate a catalyst of stable Cu clusters anchored on N-doped carbon nanosheets (c-Cu/NC), which exhibited an exceptional electroreduction for CO2 to HCOOH with a Faradaic efficiency of up to 96.2 % at current density of 276.4 mA cm−2 at − 0.96 V vs. RHE, which surpasses most reported catalysts. Especially, there was no any decay in stability during a 100 h continuous test, attributed to a strong interaction of Cu-C for restraining its self-reconstruction during CO2RR. DFT calculations indicated that N-doped carbon can strongly stabilize Cu clusters for keeping stability and cause the downshift of d-band center of Cu on c-Cu/NC for reducing the desorption energy between c-Cu/NC and OCHO* intermediates. This work provides an effective way to construct stable Cu clusters catalysts, and unveil the origin of catalyticmechanism over Cu clusters anchored on N-doped carbon towards electrochemical conversion ofCO2 to HCOOH.

CeO2 promotes electrocatalytic formic acid oxidation of Pd-based alloys

Engineering metal/oxide interface and controlling composition are the important strategies that aim towards obtaining efficient Pd-based electrocatalysts (ECs). Rationally designed ECs for dehydrogenation of formic acid play a dynamic role in the proper utilization of its chemical energy. Herein, we report Pd3M alloy nanoparticles anchored on CCeO2 (Pd3M/CCeO2, M = Cu, Ni, Co) which shows significant performance towards formic acid oxidation (FAO). Interestingly, Pd3M/CCeO2 (M = Cu, Ni, Co) ECs displayed the best FAO activity via the “dehydrogenation” pathway. The remarkable performance can be mainly attributed to the proper electronic and synergistic effects between Pd and the alloyed metal, which leads to Pd lattice contraction and downshift of d-band center. It was also observed that the FAO activity of Pd3Cu/CCeO2 is superior to that of Pd3Co/CCeO2 and Pd3Ni/CCeO2. The oxygen vacancies in CeO2 and strong Pd/CeO2 interactions established by computational and experimental studies contribute towards the overall electrocatalytic behaviour.

Unconventional s-p-d hybridization in modulating frontier orbitals of carbonaceous radicals on PdBi nanosheets for efficient ethanol electrooxidation

Rational design of highly efficient ethanol electrooxidation catalysts requires modulation of their band structure, yet most of the understanding stops at either upshift or downshift of d-band center that facilitates only a portion of ethanol oxidation reaction (EOR) process. Herein, we take in-situ formed carbonaceous intermediates as an essential part in regulating the band structure of 2D catalysts for the whole EOR process. We found that, by alloying Bi into Pd nanosheets, d band of Pd upshifted, resulting in the enhanced adsorption ability of the catalyst. After the adsorption of CH3CH2OH, p band of Bi dragged down d-band of Pd and lifted up s and p orbitals of the adsorbed carbonaceous radicals, forming molecular orbitals that bridged their energy gaps and lowered the energy barriers of electron transfer in C1 pathway. This unconventional s-p-d hybridization offers Pd14.9Bi nanosheets exhibit high mass activity of 6.6 A/mgpd and C1 selectivity of 19.7 %.

Bimetallic palladium-copper nanoplates with optimized d-band center simultaneously boost oxygen reduction activity and methanol tolerance.

The methanol-poisoning of electrocatalysts at the cathodic part of direct methanol fuel cells (DMFCs) can severely degrade the overall efficiency. Therefore, engineering cathodic catalysts with outstanding oxygen reduction activity, and simultaneously, superior methanol tolerance is greatly desired. Herein, bimetallic palladium-copper (PdCu) nanoplates with the optimized d-band center are designed as promising cathodic catalysts for DMFCs. It shows outstanding oxygen reduction activity with a mass activity (MA) of 0.522AmgPd-1 in alkaline electrolyte, overwhelming the benchmarked commercial Pt/C and Pd/C. Meanwhile, it has prominent stability with only 4.0 % loss in MA after continuous 20K cycles. More importantly, the PdCu nanoplates are almost inert toward methanol oxidation and show excellent anti-methanol capability. The theoretical calculations reveal that the downshift of d-band center in PdCu nanoplates and the electronic interaction between Pd and Cu atoms could effectively lower the methanol adsorption energy, thus leading to enhanced methanol tolerance. This work highlights the important role of tuning the electronic structure and optimized geometry of electrocatalysts to simultaneously boost their oxygen reduction activity, stability, and methanol tolerance for their future application in DMFCs.

Interface Metal Oxides Regulating Electronic State around Nickel Species for Efficient Alkaline Hydrogen Electrocatalysis.

Heterogeneous electrocatalysis typically depends on the surface electronic states of active sites. Modulating the surface charge state of an electrocatalysts can be employed to improve performance. Among all the investigated materials, nickel (Ni)-based catalysts are the only non-noble-metal-based alternatives for both hydrogen oxidation and evolution reactions (HOR and HER) in alkaline electrolyte, while their activities should be further improved because of the unfavorable hydrogen adsorption behavior. Hereto, Ni with exceptional HOR electrocatalytic performance by changing the d-band center by metal oxides interface coupling formed in situ is endowed. The resultant MoO2 coupled Ni heterostructures exhibit an apparent HOR activity, even approaching to that of commercial 20% Pt/C benchmark, but with better long-term stability in alkaline electrolyte. An exceptional HER performance is also achieved by the Ni-MoO2 heterostructures. The experiment results are rationalized by the theoretical calculations, which indicate that coupling MoO2 with Ni results in the downshift of d-band center of Ni, and thus weakens hydrogen adsorption and benefits for hydroxyl adsorption. This concept is further proved by other metal oxides (e.g., CeO2 , V2 O3 , WO3 , Cr2 O3 )-formed Ni-based heterostructures to engineer efficient hydrogen electrocatalysts.

Cation/anion-doping induced electronic structure regulation strategy to boost the catalytic hydrogen evolution from ammonia borane hydrolysis

Exploration of high-performance and cost-effective catalysts for hydrogen production from chemical hydrogen-storage materials is vital but still a challenge. Herein we report the synthesis of a ZIF-67 derived Co3O4 nanoparticles in a carbon-based nanoframeworks and discover that doping phosphorus into Co3O4 has a unique electronic structure modulation effect, resulting in a nearly 29-fold enhancement of the catalytic activity for ammonia borane hydrolytic dehydrogenation. Furthermore, combining the P doping with Cu doping, a strong synergistic effect is realized to boost the catalytic H2 generation with an astonishing nearly 51-fold improvement (turnover frequency, TOF = 35.6 min−1). Based on the experimental and theoretical results, the enhanced performance is attributed to the optimization of the electronic configuration and the downshift of d-band center over Co3O4 after P/Cu doping, thereby facilitating H2O dissociation and hydrogen desorption. This work will be applicable to designing other metal based nanocatalysts toward more efficient energy conversion reactions.

Boosting Electrocatalytic Activity of Single Atom Catalysts Supported on Nitrogen-Doped Carbon through N Coordination Environment Engineering.

Nonprecious group metal (NPGM)-based single atom catalysts (SACs) hold a great potential in electrocatalysis and dopant engineering has been extensively exploited to boost their catalytic activity, while the coordination environment of dopant, which also significantly affects the electronic structure of SACs, and consequently their electrocatalytic performance, have been largely ignored. Here, by adopting a precursor modulation strategy, the authors successfully synthesize single cobalt atom catalysts embedded in nitrogen-doped carbon, Co-N/C, with similar overall Co and N concentrations but different N types, that is, pyridinic N (NP ), graphitic N (NG ), and pyrrolic N (NPY ). Co-N/C with the Co-N4 moieties coordinated with NG displays far superior activity for oxygen reduction (ORR) and evolution reactions, and superior activity and stability in both zinc-air batteries and proton exchange membrane fuel cells. Density functional theory calculation indicates that coordinated N species in particular NG functions as electron donors to the Co core of Co-N4 active sites, leading to the downshift of d-band center of Co-N4 and weakening the binding energies of the intermediates on Co-N4 sites, thus, significantly promoting catalytic kinetics and thermodynamics for ORR in a full pH range condition.

Changes of Oxygen Adsorption State of Pt Nanoparticle Catalyst on the Carbon Support By the Ion Irradiation

Pt nanoparticles (NPs) on an Ar+-irradiated glassy carbon (GC) substrate were recently found to show a higher oxygen reduction reaction (ORR) activity than those on the non-irradiated one [1]. This finding suggests that the Pt nanoparticles would be electronically modified by vacancy introduction due to the irradiation into GC. Our theoretical research revealed that vacancies in graphite would lower a d-band center of the Pt nanoparticles [2]. The downshift of d-band center of Pt 5d electrons leads to higher ORR activity because the downshift causes the downshift of the antibonding orbital level of the oxygen adsorbed states of Pt (Pt-O) closing to Fermi level and then results in weaker Pt-O bond [3]. However, it has not been revealed whether the Pt-O antibonding level of Pt NPs is downshifted by the ion irradiation into the carbon support. Therefore, we performed in situ x-ray absorption fine structure (XAFS) measurements, which can observe the unoccupied states of the Pt 5d orbital binding with the adsorbed oxygen, of Pt NPs on the irradiated GC and derived the oxygen adsorbed surface states.The GC substrates were irradiated with 380 keV Ar+ at the fluences of 7.5×1015 ions/cm2 in the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of the Takasaki Advanced Radiation Research Institute. The Pt nanoparticles were then deposited by RF magnetron sputtering. The Pt deposition was also done on the non-irradiated GC substrates for comparison. The XAFS spectra were measured at BL14B1 in SPring-8. We first measured the XAFS spectra of the irradiated and non-irradiated samples reduced by 1 atm. 100 °C H2 (10%) + He (90%) gas flowing at 100 ml/min for 10min. Then the samples were exposed under mixed gas with O2 + He gas flowing at 100 ml/min at room temperature to adsorb the oxygen to Pt nanoparticles and were measured XAFS spectra. In order to observe the oxygen adsorbed surface states of Pt NPs, we derived the Dm spectra by the subtraction from the XANES spectra after the reduction from the those during the oxygen exposure.Figure 1 shows the Dμ spectra for the Pt/GC and Pt/irradiated GC together with the results of peak fitting. In the non-irradiated sample, we could fit using one peak at around 11562 eV (denoted as peak 1), whereas needed peak 1 in addition to peak 2 on the higher energy side. Since the Dμ spectra represent the change of the electronic state in Pt by oxygen adsorption, the convex peak means that new electronic states are formed at the energy position by the oxygen adsorption. The main peak (peak 1) is the antibonding level of the oxygen adsorbed Pt (Pt-O). On the other hand, the peak 2 is considered to be an oxide species that is more strongly bind to oxygen than Pt-O. It needs future study to elucidate its origin.Comparing the peak 1 of the non-irradiated and the irradiated sample, we found that the peak position for the irradiated sample is 0.7 eV lower than that for the non-irradiated one. This indicates that the Pt-O antibonding level shifts toward low energy and gets close to the Fermi level. Thus, the shift leads to easy electron filling to the antibonding level and thus to a weaker Pt-O bond. In this presentation, we will discuss the change of electronic structure of Pt nanoparticles by the ion irradiation in detail.

Biaxial strained dual-phase palladium-copper bimetal boosts formic acid electrooxidation

Surface strain engineering is considered as an effective strategy to promote the electrocatalytic properties of noble metal nanocrystals. Herein, we construct a dual-phase palladium-copper (DP-PdCu) bimetallic electrocatalyst with remarkable biaxial strain via a one-pot wet-chemical approach for formic acid oxidation. The biaxial strain originates from the lattice mismatch between the disordered face-centered cubic (FCC) phase and ordered body-centered cubic (BCC) phase in each of DP-PdCu nanoparticles. The proportion of FCC and BCC phases and size of PdCu nanoparticles are dependent on the addition amount of capping agent, cetyltrimethylammonium bromide (CTAB). Density functional theory calculations reveal the downshift of d-band center of Pd atoms due to the interfacial strain, which weakens the adsorption strength of undesired intermediates. These merit the DP-PdCu catalyst with superior mass activity of 0.55 A·mgPd-1 and specific activity of 1.91 mA·cmPd-2 toward formic acid oxidation, outperforming the single FCC/BCC PdCu and commercial Pd/C catalysts. This will provide new insights into the structure design of high-performance electrocatalysts via strain engineering.

Uncovering the Role of Countercations in Ligand Exchange of WSe2: Tuning the d-Band Center toward Improved Hydrogen Desorption

The role of countercations that do not bind to core nanocrystals (NCs) but rather ensure charge balance on ligand-exchanged NC surfaces has been rarely studied and even neglected. Such a scenario is unfortunate, as an understanding of surface chemistry has emerged as a key factor in overcoming colloidal NC limitations as catalysts. In this work, we report on the unprecedented role of countercations in ligand exchange for a colloidal transition metal dichalcogenide (TMD), WSe2, to tune the d-band center toward the Fermi level for enhanced hydrogen desorption. Conventional long-chain organic ligands, oleylamine, of WSe2 NCs are exchanged with short atomic S2- ligands having countercations to preserve the charge balance (WSe2/S2-/M+, M = Li, Na, K). Upon exchange with S2- ligands, the charge-balancing countercations are intercalated between WSe2 layers, thereby serving a unique function as an electrochemical hydrogen evolution reaction (HER) catalyst. The HER activity of ligand-exchanged colloidal WSe2 NCs shows a decrease in overpotential by down-shift of d-band center to induce more electron-filling in antibonding orbital and an increase in the electrochemical active surface area (ECSA). Exchanging surface functionalities with S2- anionic ligands enhances HER kinetics, while the existence of intercalated countercations improves charge transfer with the electrolyte. The obtained results suggest that both anionic ligands and countercationic species in ligand exchange must be considered to enhance the overall catalytic activity of colloidal TMDs.

In-Situ doping-induced crystal form transition of amorphous Pd–P catalyst for robust electrocatalytic hydrodechlorination

Developing catalysts with high activity and high atom utilization as well as exploring catalytic active sites are the biggest challenges for the electrocatalytic hydrodechlorination technology. Herein, a novel strategy of Pd crystal transformation induced by in-situ doping was proposed, and a series of amorphous Pd–P nanoparticles (NPs) with controllable coordination environment were synthesized successfully. The amorphous Pd–P NPs catalyst exhibits the highest activity for electrocatalytic hydrodechlorination and good cycling stability when the Pd–P coordination number is 3 and the Pd–Pd coordination number is 4. The 4-chlorophenol hydrodechlorination efficiency of Pd–P-60 NPs reaches 100 % within 2 h, and the mass activity is 8.58 min−1 g−1, which is 5.57 times as high as that for crystalline Pd NPs catalyst. Theoretical calculation shows that Pd–P catalyst facilitates the desorption of phenol and weakens the toxic effect on active sites. Density of states indicate that the doping of P results in a downshift of d-band center, facilitating the desorption of phenol. This work discovers the crystal effect and coordination effect of amorphous Pd–P NPs for electrocatalytic hydrodechlorination, which lays an important theoretical foundation for the design and development of high-performance Pd-based catalysts for electrocatalytic hydrodechlorination.

Selective hydrogenation of acetylene over Pd-Sn catalyst: Identification of Pd2Sn intermetallic alloy and crystal plane-dependent performance

In Pd catalyzed acetylene semi-hydrogenation, high selectivity always comes at the expense of activity while improving both selectivity and activity is challenging. In this work, the performance of Pd alloy catalysts was enhanced by inserting Sn phase to modify both surface Pd ensembles and electronic structures. Compared with Pd/C, the optimal Pd2Sn/C catalyst exhibits higher selectivity at the same acetylene conversion level, with its selectivity increased from 10 % to nearly 95 % at ca 100 % acetylene conversion. Both experimental and DFT calculation results reveal that the specific performance is attributed to the redispersion of surface Pd ensembles by Sn insertion and down-shift of d-band center of catalysts, thus changing the adsorption behavior of the reaction gases. This design principle provides an efficient method for tailoring and optimizing durable Pd-based catalysts with desirable reactivity and ethylene selectivity for selective hydrogenation of acetylene.

Electronic structure and d-band center control engineering over M-doped CoP (M = Ni, Mn, Fe) hollow polyhedron frames for boosting hydrogen production

The practical application of hydrogen evolution reaction (HER) through water splitting depends on the development of low cost and efficient non-noble-metal catalysts. As a potential electrocatalyst, the improvement of HER performance catalyzed by nanostructured transition metal phosphides still remains a great challenge. Tuning the novel nanostructure, morphology, and electronic state from nanoscale is of great important to achieve highly efficient HER electrocatalysts. Herein, we first developed an electronic structure and d-band center control engineering for accelerating the HER process in both acid and alkaline media over M-doped CoP (M = Ni, Mn, Fe) hollow polyhedron frames (HPFs), which were synthesized by a self-templating transformation (STT) strategy. Impressively, the HER electrocatalytic activity can be maximumly promoted and maintained at least 21 h for Ni-CoP/HPFs catalyst. Synchrotron-based X-ray absorption near-edge structure, X-ray photoelectron spectroscopy, auger electron spectroscopy, ultraviolet photoemission spectroscopy and density functional theory calculations consistently reveal the improved performance is attributed to the changes of the electronic structure and the downshift of d-band center after metal doping. The Ni-CoP/HPFs catalyst also indicates excellent activity with a cell voltage of 1.43 V to achieve the current density of 10 mA cm−2 and superior stability when it was employed as a cathode for HER and an anode for urea oxidation in 1 M KOH with 0.5 M urea. The success modulation of HER performance in current STT strategy will provide a promising pathway for designing various transition metal-doped compounds for energy-related catalysis processes.

Ultradispersed Nickel Phosphide on Phosphorus-Doped Carbon with Tailored d-Band Center for Efficient and Chemoselective Hydrogenation of Nitroarenes

Nickel phosphide is a promising catalyst for hydrogenation of nitroarenes but suffers from sluggish H desorption and low chemoselectivity. Herein, we overcome these problems through reducing the Ni2P into subnanosized clusters, tailoring the d-band center of Ni, and coupling them with P-doped carbon. Using density functional theory (DFT) calculations, we predicted that electron transfer from P-doped carbon to Ni2P cluster results in downshift of d-band center of Ni that promotes H desorption on highly charged antibonding orbital of Ni–H, and reactant is preferentially adsorbed on P-doped carbon surface through nitro group due to the geometrical hindrance on Ni2P clusters that leads to good selectivity. Then we developed a chemical anchoring method to fabricate Ni2P supported on P-doped carbon with high dispersion of 81.3%. The synthesized catalyst delivers high activity and selectivity chemoselective hydrogenation of nitroarenes, and outperforms various noble- and transition-metal catalysts. Moreover, we revealed the origins of the superior performance of catalyst by characterizations, and confirmed the conclusion of DFT calculation. Such concept of tailoring d-band center and improving dispersion of active phase can provide insight for design of catalysts for hydrogenation and beyond.

High oxygen reduction activity of TM13@Pt134 and TM12N@Pt134 (TM=Ti, V, Mn, Fe, Co, Ni, and Cu) core-shell electrocatalysts studied by first-principles theory

Core-shell catalysts are effective to improve the stability of Pt in the oxygen reduction reaction (ORR). Adding nitrogen (N) into transition metal (TM) core is a novel way for the substantial reduction in Pt loading while retaining high ORR activity. Core-shell electrocatalysts containing Pt shell with TM (TM = Ti, V, Mn, Fe, Co, Ni, and Cu) and transition metal nitride (TMN) cores were investigated using density functional theory (DFT). The dissolution potential, binding energy of oxygen (BE-O) and hydroxyl (BE-OH), surface strain, and d-band center were calculated on TM13@Pt134 and TM12N@Pt134 catalysts in oder to investigate the stability and ORR activity. The calculation results indicated that compared to the corresponding non-nitrogen nanoparticles, TMN cores resulted in higher dissolution potential and surface strain, lower BE-O, and downshift of d-band center. Among the investigated catalysts, Cu12N@Pt134 showed a comparable activity with pure Pt catalyst. The former preferred a dissociative mechanism to an associated mechanism in the ORR pathway, with the Gibbs free energy change (ΔG) of 0.88 V in the rate-determining step. This study will contribute to the accurate identification and innovative design of promising core−shell electrocatalysts toward ORR in fuel cell applications.

Coverage Effect on the Activity of the Acetylene Semihydrogenation over Pd–Sn Catalysts: A Density Functional Theory Study

The existence of acetylene impurities in ethylene feedstock is harmful to downstream polymerization reactions. The removal of acetylene can be achieved via semihydrogenation reaction, which is normally catalyzed by Pd-based catalysts. This paper describes the coverage effect on the activity of acetylene hydrogenation reactions over Pd and PdSn alloy surfaces. High-coverage models are presented to construct coverage-dependent adsorption energies of C2H2, C2H4, and H2 on Pd(111) and Pd3Sn(111) surfaces. It has been validated that the downshift of d-band center caused by preadsorbed molecules makes the adsorption weaker along with the increase of coverage, and the geometric effect can be neglected. An iterative method has been applied to predict surface coverages of reaction intermediates. Previous calculations with low-coverage models indicate that alloying Pd with late or post-transition metals, in general, enhances ethylene selectivity, accompanied with lower hydrogenation activity. However, by applying a...