Shift Of D-band Center Research Articles

Ab-Initio and Experimental Study of Oxygen Reduction Reaction (ORR) Activity and Durability of Ordered PtNi/C Catalysts

Developing durable and highly active low-Pt electrocatalysts for oxygen reduction reaction (ORR) in acidic media is necessary for highly effective polymer electrolyte membrane fuel cells (PEMFCs). Intermetallic structure is thermodynamically more stable than random alloy metal compounds. In oxygen reduction reaction (ORR), Pt3Ni1 with (111) facet is to be the most effective electrocatalyst for ORR. Therefore, to develop a highly efficienct electrocatalyst for oxygen reduction reaction (ORR) in effective polymer electrolyte membrane fuel cell (PEMFC), an ordered PtNi/C intermetallic alloy on a carbon black support has been designed. To enhance ORR performance and reduce Pt usage, a Pt-transition metal alloy catalyst has been developed. Alloying Pt with a second metal on a carbon support material can improve activity due to the change in lattice parameter and the electronic effect. According to the d-band theory, the downshift effect of the d-band induced by the upshift of the fermi level is predicted to improve ORR activity by weakening the binding energy. In case of alloying Pt and Ni, it can be predicted that the difference in electronegativity between Pt and Ni will induce a fermi level shift, resulting in a d-band center shift effect, which can enhance ORR activity. Compared to random alloy structured electrocatalysts, intermetallic structures of ordered PtNi were more thermodynamically stable. Moreover, intermetallic structure stabilizes the alloy, improving the durability of metal components against chemical corrosion in acidic media, such as HClO4 or H2SO4. Therefore, to improve catalyst’s durability, heat treatment was used to align the structure, making it structurally stable and reducing Pt-Pt distance. Heat treatment screening was carried out between 500℃ and 800℃ using a thermal shock method to minimize particle size growth. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disc electrode (RDE) were used to investigate the compositional difference and crystallinity of the intermetallic structure, electrochemical ORR activity and durability between disordered PtNi/C (d-PtNi/C) and ordered PtNi/C (o-PtNi/C). The electronic effect of the three Nicore@Ptshell models, namely ordered Nicore@Ptshell (o-PtNi), disordered Nicore@Ptshell (d-PtNi), and pure Pt147 (pure Pt), was estimated through density functional theory (DFT). The d-band theory and Bader charge analysis were used to estimate ORR activity and charge transfer, respectively. Additionally, the durability in acidic media of each model was estimated through dissolution potential calculations (Udiss). This work has supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT in Republic of Korea (MSIT) (NRF-2022R1A2C2093090). This work was supported by the Technology Innovation Program (20019175) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). This research was supported by the Ministry of Trade, Industry, and Energy (MOTIE), Korea, under “Digital manufacturing platform" (No. P0022331) supervised by the Korea Institute for Advancement of Technology (KIAT).

Synergistic Electronic Interaction in PdCu Alloy/TiO2-NSs for Ambient Efficient Dehydrogenation of Formic Acid.

Palladium-based catalysts are remarkable in endorsing hydrogen (H2) generation through formic acid (HCOOH, FA) dehydrogenation under near-ambient conditions. Hydrogen energy efficiency depends on high-performance catalyst design. In this study, Pd-Cu nanoalloy catalysts with mutable atomic ratios are successfully fabricated on TiO2 nanosheets (TiO2-NSs).The synergistic electronic interactions between Palladium (Pd) and copper (Cu) are revealed through a density of states (DOS) analysis of alloy supported over a mixed valence state of Ti linked to oxygen vacancies (Vo) in TiO2-NSs, Enhanced adsorption of target molecules reveals novel active sites for Formic acid dehydrogenation (FAD), with O─H bond cleavage via HCOO formate intermediate preceding C─H and C─O bond cleavage. Experimental and theoretical research demonstrates that the Pd-Cu/TiO2-NSs (3:7) catalyst d electron redistribution and d-band center shift lower the activation energy for O─H bond cleavage, exhibit superior H2 production than pure Pd and Cu, increasing Pd electron density due to synergistic effects from reactive crystal facets, defects, and strong metal support interactions (SMSI), lowering the activation energy for HCOOH dissociation step, generating carbon dioxide (CO2) and H2 with a unprecedented high turnover frequency (TOF) of 6268 molH2.h-1.molPd-1 at 303K with activation energy (Ea) of 15 KJ mol-1. This attempt models an efficient HCOOH-to-hydrogen catalyst.

Advanced N-doping nickel-cobalt phosphides for boosting hydrogen evolution in acid and alkali media

In this article, the hydrogen evolution performance in 0.5 M H2SO4 and 1.0 M KOH is improved by introducing N atoms into Ni2P/Co2P through high-temperature doping (N–Ni2P/Co2P). N–Ni2P/Co2P has a lower overpotential than Ni2P/Co2P, which can achieve cathodic current densities of 10 mA cm−2, 100 mA cm−2 at overpotentials of 48 mV, 228 mV in 1.0 M KOH and 63 mV, 211 mV in 0.5 M H2SO4. Density functional theory (DFT) results found that the introduction of N atoms changed the electronic structure of the catalyst. Due to the forward shift of d-band center, the binding force between the catalyst and H∗ is enhanced, providing favorable conditions for hydrogen evolution. Furthermore, the results of scaled-up tests show that 5 cm × 5 cm N–Ni2P/Co2P electrodes still exhibit superior performance, revealing a prospect of industrialization.

Strong electronic metal-support interaction of Ni4Mo/N-SrMoO4 promotes alkaline hydrogen electrocatalysis

Ni4Mo electrocatalyst stands out as the promising candidate for hydrogen evolution/oxidation reaction (HER/HOR), yet the intensive hydrogen adsorption leads to sluggish kinetics, decreasing hydrogen catalysis efficiency. Herein, the structure of Ni4Mo nanoparticles anchored on wafer-biscuit-like N-SrMoO4 nanorods (Ni4Mo/N-SrMoO4) is developed to accelerate reaction kinetics by modulating electronic structure. The designed N-SrMoO4 support enables strong electronic metal-support interaction with Ni4Mo, resulting in a downward shift of d-band center and achieving thermally neutral hydrogen adsorption. Ni4Mo/N-SrMoO4 exhibits HER performance with an ultralow overpotential of 15 mV at 10 mA cm−2, superior to Pt/C (η10=18 mV). The outstanding exchange current density of 10.2 mA cm−2 for HOR is three times higher than that of Pt/C (3.5 mA cm−2). Ni4Mo/N-SrMoO4 is further assembled in anion exchange membrane water electrolyzer (AEMWE), resulting in a current density of 100 mA cm−2 at voltage of 1.71 V and the excellent stability of 300 hours. Theoretical calculations and in-situ spectroscopy indicate that the introduction of Sr in N-SrMoO4 effectively enhances electronic metal-support interaction, facilitates the enrichment of adsorbed hydroxyl (OHads) on active sites and weakens hydrogen adsorption on Ni4Mo, thereby accelerating reaction kinetics of hydrogen electrocatalysis.

Fluorine atoms incorporation strengthens the strong metal-support interaction of PtNi@NFGC for enhanced methanol oxidation reaction performance under alkaline media

The regulatory mechanism of strong metal-support interaction (SMSI) is of great significance in improving the electrocatalytic performance for supported electrocatalysts. Here, PtNi alloy nanoparticles were deposited on N, F-codoped graphene-like carbon nanosheets (PtNi@NFGC) to construct a highly active interface for efficient methanol oxidation reaction (MOR), which solves the problems of high cost, poor activity and easy aggregation of Pt-based catalysts. Due to the high electrophilicity, F atoms doping into the carbon lattice can not only manipulate the electron structure and the state of the carbon skeleton, but also further trigger the stronger charge transfer between metal atoms and carbon support. Compared with single-doped PtNi@NGC, N, F-codoped PtNi@NFGC possesses a lower onset potential and methanol oxidation potential, higher methanol oxidation current and stronger CO tolerance. The results of the partial density of state (PDOS) simulation display that N, F-codoping promotes the electron transfer from Pt atoms to NFGC support, and leads to the d-band center shift upward, thus strengthening the oxidation degree of Pt active sites and increasing the composition of high-valent Ptx+. In-situ Raman analysis and density functional theory (DFT) results expound that F atoms embedding observably enhances the adsorption energy of Pt active centers to *OH intermediates, which not only significantly improves MOR catalytic activity, but also achieves efficient methanol dehydrogenation and alleviates CO poisoning. This customization of metal-support interface interaction by heteroatom doping strategy opens up opportunities for designing efficient supported catalysts.

Steric interaction of iridium sites towards efficient oxygen and hydrogen evolution

Transition metal materials that loaded with trace of Iridium (Ir) are widely accepted as effective catalysts for oxygen evolution (OER) and hydrogen evolution reaction (HER), in which the Ir atoms exposed on the surface can directly affect the electrocatalytic reaction. However, this neglects the Ir – Ir interaction of distinct locations, which may be benefit for the fine-tuning of electronic structure. Herein, we changed the locations (surface and inside) of Ir atoms in the cobalt oxide (Co3O4@NC), and investigated their alkaline OER and HER performances. Combined with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and theoretical calculations, we infer that the steric interaction induced by the surface – internal Ir sites can weaken the Ir-O bond and optimize the adsorption of intermediates on catalyst surface with a negative shift of d-band center, enabling the surface-Ir sites with lower energy barrier for water dissociation and hydrogen adsorption for HER. Therefore, the as-prepared Irw-Co3O4@NC with surface − inside Ir distribution significantly improve the HER without degrading OER performance, with low overpotential of −173 / −71 mV for HER at −10 mA/cm2 in 0.1 M KOH / 1.0 M KOH, and 244 / 249 mV at 10 mA/cm2 for OER.

FeN3S1─OH Single-Atom Sites Anchored on Hollow Porous Carbon for Highly Efficient pH-Universal Oxygen Reduction Reaction.

Regulating the asymmetric active center of a single-atom catalyst to optimize the binding energy is critical but challenging to improve the overall efficiency of the electrocatalysts. Herein, an effective strategy is developed by introducing an axial hydroxyl (OH) group to the Fe─N4 center, simultaneously assisting with the further construction of asymmetric configurations by replacing one N atom with one S atom, forming FeN3S1─OH configuration. This novel structure can optimize the electronic structure and d-band center shift to reduce the reaction energy barrier, thereby promoting oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities. The optimal catalyst, FeSA-S/N-C (FeN3S1─OH anchored on hollow porous carbon) displays remarkable ORR performance with a half-wave potential of 0.92, 0.78, and 0.64V versus RHE in 0.1m KOH, 0.5m H2SO4, and 0.1m PBS, respectively. The rechargeable liquid Zn-air batteries (LZABs) equipped with FeSA-S/N-C display a higher power density of 128.35mWcm-2, long-term operational stability of over 500h, and outstanding reversibility. More importantly, the corresponding flexible solid-state ZABs (FSZABs@FeSA-S/N-C) display negligible voltage changes at different bending angles during the charging and discharging processes. This work provides a new perspective for the design and optimization of asymmetric configuration for single-atom catalysts applied to the area of energy conversion and storage.

Effect of stoichiometric ratio of rhodium antimonide intermetallic compounds on the performance of electrocatalysis to the hydrogen oxidation reaction and CO-tolerance

Binary intermetallic compounds (BIMCs) play a significant role in various catalytic systems. However, the synthesis of BIMCs with different stoichiometric ratios remains challenging, and the corresponding studies toward catalytic performance are scarce. Herein, three kinds of pure-phase rhodium antimonide BIMCs (Rh2Sb, RhSb, and RhSb2) were successfully fabricated. Interestingly, Rh2Sb BIMC shows the highest activity and long-time stability toward hydrogen oxidation reaction (HOR) in alkaline condition among the prepared samples, reaching a mass normalized kinetic current density of 2.04 A mgPGM-1 (PGM: platinum group metal), which is 7.6 times higher than that of commercial Pt/Ccom. However, the CO-tolerance performances under 1000 ppm CO/H2 follows the order: RhSb > Rh2Sb > RhSb2. Combined with the theoretical calculations, the shift of d-band center of RhxSby BIMCs depends on the Sb content. Accordingly, RhxSby BIMCs with different stoichiometric ratio display varied adsorption energy of *OH, *H and CO, giving rise to the individual HOR activity and resistance to CO poisoning. This work sheds a light on designing efficient BIMCs catalysts for energy conversion.

Coordination Engineering Induced d-Band Center Shift on Single-Atom Fe Electrocatalysts for Enhanced Oxygen Reduction.

Part of the performance of single-atom catalysts (SACs) is greatly influenced by the microenvironment around a single metal site, of which the oxygen reduction reaction (ORR) is counted as one of them. However, an in-depth understanding of the catalytic activity regulation by the coordination environment is still lacking. In this study, a single Fe active center with axial fifth hydroxyl (OH) and asymmetric N,S coordination embedded in a hierarchically porous carbon material (Fe-SNC) are prepared. Compared to Pt/C and most of the reported SACs, as-prepared Fe-SNC has certain advantages in terms of ORR activity and maintains sufficient stability. Furthermore, the assembled rechargeable Zn-air battery exhibits impressive performance. The combination of multiple findings revealed that the introduction of S atoms not only facilitates the formation of porous structures but also facilitates the desorption and adsorption of oxygen intermediates. On the other hand, with the introduction of axial OH groups, the bonding strength of the ORR intermediate is reduced, and even the central position of the Fe d-band is optimized. The developed catalyst is expected to lead to further research on the multiscale design of the electrocatalyst microenvironment.

Tuned d-band states over lanthanum doped nickel oxide for efficient oxygen evolution reaction

The d-band state of materials is an important descriptor for activity of oxygen evolution reaction (OER). For NiO materials, there is rarely concern about tuning their d-band states to tailor the OER behaviors. Herein, NiO nanocrystals with doping small amount of La3+ were used to regulate d-band states for promoting OER activity. Density of states calculations based on density functional theory revealed that La3+ doping produced upper shift of d-band center, which would induce stronger electronic interaction between surface Ni atoms and species of oxygen evolution reaction intermediates. Further density functional theory calculation illustrated that La3+ doped NiO possessed reduced Gibbs free energy in adsorbing species of OER intermediate. Predicted by theoretical calculations, trace La3+ was introduced into crystal lattice of NiO nanoparticles. The La3+ doped NiO nanocrystal showed much promoted OER activity than corresponding pristine NiO product. Further electrochemical analysis revealed that La3+ doping into NiO increased the intrinsic activity such as improved active sites and reduced charge transfer resistance. The in-situ Raman spectra suggested that NiO phase in La3+ doped NiO could be better maintained than pristine NiO during the OER. This work provides an effective strategy to tune the d-band center of NiO for efficient electrocatalytic OER.

Engineering d-band states of (CuGa)xZn1-2xGa2S4 material for photocatalytic syngas production

The d-band states of catalytic materials participate in adsorbing reactive intermediate species and determine the catalytic behaviors in CO2 reduction reactions. However, surface d-band states relating to the photocatalytic CO2 reduction reactions behaviors are rarely concerned. Herein, a slightly amount of Cd2+ is decorated on the surface of (CuGa)xZn1-2xGa2S4 material (Cd2+/(CuGa)xZn1-2xGa2S4) to tune the surface d-band states for improved CO2 reduction reactions. The Cd2+/(CuGa)xZn1-2xGa2S4 is fabricated via the facile ions-exchange method to make that slightly Zn2+ is substituted by Cd2+. The Cd2+/(CuGa)xZn1-2xGa2S4 exhibits much enhanced photocatalytic activity in CO2 reduction reactions to produce CO and water splitting to produce H2. Physical characterizations show that the energy band structure is not changed obviously. Density functional theory reveals that Cd2+/(CuGa)xZn1-2xGa2S4 possesses a closer shift of d-band center to Fermi level than (CuGa)xZn1-2xGa2S4, suggesting easier adsorption of CO2 reduction reactive intermediates after Cd2+ decoration. Further calculations confirm that a relatively reduced adsorption Gibbs energy of reactive intermediates in CO2 reduction reaction is required on Zn atoms in Cd2+/(CuGa)xZn1-2xGa2S4 material, benefiting the photocatalytic CO2 reduction reactions. This work engineers surface d-band states by surface Cd2+ decoration, which gives an effective strategy to design highly efficient photocatalysts for syngas production.

General strategy for evaluating the d-band center shift and ethanol oxidation reaction pathway towards Pt-based electrocatalysts

General strategy for evaluating the d-band center shift and ethanol oxidation reaction pathway towards Pt-based electrocatalysts

Electronic Modulation of the Interaction between Fe Single Atoms and WO2.72–x for Photocatalytic N2 Reduction

In the design of photocatalysts for ammonia synthesis, the construction of effective nitrogen (N2) adsorption and activation sites is critical. Herein, Fe single atoms were effectively fixed on the surfaces of WO2.72–x nanowires. Electronic interactions between single Fe atoms and WO2.72–x resulted in a d-band center shift toward the Fermi level and thus enhancement of N2 bonding with the catalyst surface. The studies of differential charge density and electron localization reveal that there is enhanced electron transfer from Fe-SA/WO2.72–x to the adsorbed N2, signifying that Fe single atoms are active centers for N2 activation. Benefiting from electronic interactions, the optimized catalyst shows a NH4+ generation rate of 186.5 μmol g–1 h–1 during photocatalytic N2 reduction.

Engineering asymmetric Fe coordination centers with hydroxyl adsorption for efficient and durable oxygen reduction catalysis

Single-atom Fe catalysts are a promising substitute to Pt catalysts for oxygen reduction reaction (ORR). Adjusting metal energy level through direct atomic interface regulation can effectively improve catalytic performance but still in its infancy. Herein, highly active nitrogen and sulfur dual-coordinated asymmetric Fe center anchored in carbon nanoparticles were developed. Spontaneously absorbed OH ligand is steadily anchored in asymmetric atomic interface, constructing new FeN3S-OH moiety. Theoretical calculations reveal that the incorporated S atom combined with OH ligand as energy level modifier effectively activate Fe center by electronic modulation and d-band center shift, rendering improved ORR activity of FeNSC-2Fe with E1/2 of 0.913 V in alkaline, 0.806 V in acidic and 0.711 V in neutral media. The FeNSC-2Fe-based device displays high power density of 306 mW cm−2 in Zn-air battery and 2485 mW m−2 in microbial fuel cell. This work provides a new perspective for the controllable synthesis and performance optimization for electrocatalysts.

Significantly enhanced oxygen evolution reaction performance by tuning surface states of Co through Cu modification in alloy structure

• A binder- and carbon-free OER catalyst of a series of Co x Cu 1-x alloys is developed. • The role of composition controlling and electronic perturbation on OER performance is investigated. • The catalyst reconstruction process, during OER, is investigated. • Surface oxygen containing substances not only promote the activity of Co x Cu 1-x alloys, but also increase the durability. • The role d-band center shifting on OER activity of Co x Cu 1-x alloys is captured. The design of high efficiency, low cost and abundant sources electrocatalysts for oxygen evolution reaction (OER) has attracted more and more attention, because of the depletion of precious and rare metals. Herein, we reported a highly active Co 0.7 Cu 0.3 alloy, which screening from a series of Co x Cu 1-x alloys (x = 0.1–0.9) via surface composition controlling and electron state modification. Compared with the Co, other Co x Cu 1-x alloys, as well as commercial RuO 2 /IrO 2 , the Co 0.7 Cu 0.3 catalyst exhibited very high activity in electrocatalytic O 2 production from alkaline solution (∼207 mV overpotential). Meanwhile the Co 0.7 Cu 0.3 catalyst exhibited excellent durability for OER, after 72,000 s operation, the attenuation rate of Co 0.7 Cu 0.3 catalyst is lower than ∼ 20%. The high catalytic activity of Co 0.7 Cu 0.3 is attributed to positive shift of d-band center and surface species of Co 0.7 Cu 0.3 alloy which facilitates oxygen-containing species (OCS) formation (*H 2 O 2 , *OOH, *OH) and electron transfer. This method of improving the catalytic performance by adjusting the alloy composition to achieve the microscopic electronic perturbation effect is expected to attract attention in the later research.

Surface phase stability of surface segregated AgPd and AgCu nanoalloys in an oxygen atmosphere

The geometric structure of 38-atom AgPd and AgCu nanoalloys is obtained by the genetic algorithm and density functional theory for all compositions and their surface phase stability diagrams are established to provide a clear image for the initial oxidation process. Ag surface segregation is confirmed for both AgPd and AgCu nanoalloys in vacuum. Pure Pd and Cu nanoparticles have lower surface phase stability than bulk metals to be oxidized and the alloying can improve the oxidation resistance. Segregated AgCu nanoalloys have higher phase stability than mixed AgCu in vacuum and have lower surface phase stability than mixed AgCu nanoalloys in an oxygen atmosphere. Unexpectedly, segregated AgPd nanoalloys have both higher phase stability in vacuum and higher surface phase stability in an oxygen atmosphere than that of mixed AgPd nanoalloys. The higher surface phase stability of segregated AgPd nanoalloy could be attributed to the slight elevation of Pd Milliken charge and negative shift of d-band center. Compared with the selective oxidation in conventional alloy oxidation models where the selective oxidation is related to alloy composition, the nanoalloy oxidation is proposed to correlate with surface segregation in AgPd and AgCu nanoalloys in this work, which promotes the development of the conventional alloy oxidation models in that the surface segregation is a precursor to the surface oxidation of nanoalloy and plays a critical role in the selective oxidation of nanoalloy.

Insights into the Pt (111) Surface Aid in Predicting the Selective Hydrogenation Catalyst

The d-band center position of the metal catalyst is one of the most important factors for catalytic selective hydrogenation, e.g., the conversion of nitrostyrene to aminostyrene. In this work, we modulate the d-band center position of the Pt surface via H coverage manipulation in order to assess the highly efficient selective hydrogenation catalyst using density functional theory (DFT) calculation, which is validated experimentally. The optimal transition metal catalysts are first screened by comparing the adsorption energy values of two ideal models, nitrobenzene and styrene, and by correlating the adsorption energy with the d-band center positions. Among the ten transition metals, Pt nanoparticles have a good balance between selectivity and the conversion rate. Then, the surface hydrogen covering strategy is applied to modulate the d-band center position on the Pt (111) surface, with the increase of H coverage leading to a decline of the d-band center position, which can selectively enhance the adsorption of nitro groups. However, excessively high H coverage (e.g., 75% or 100%) with an insufficiently low d-band center position can switch the chemisorption of nitro groups to physisorption, significantly reducing the catalytic activity. Therefore, a moderate d-band center shift (ca. −2.14 eV) resulted in both high selectivity and catalytic conversion. In addition, the PtSn experimental results met the theoretical expectations. This work provides a new strategy for the design of highly efficient metal catalysts for selective hydrogenation via the modulation of the d-band center position.

Highly Active and Durable Pt-Doped Nanoporous Au-Cu Catalysts for Formic Acid Oxidation

A substantial work has been done in the field of electrocatalysis to address all known drawbacks of Pt-based catalysts and to ultimately improve their activity and durability in the formic acid oxidation (FAO) process. Among the entertained approaches, alloying of Pt with other metals has been key for achieving better performance. Bi-metallic catalysts such as Pt-Ru, Pt-Cu, Pt-Au, Bi decorated Pt, Pt-Pd and Pt-Ag were synthesized in order to achieve better activity by suppressing the dehydration pathway. Alternatively, some researchers focused on studying the application of Pd nanoparticles or Pd based nano-alloys due to palladium’s preference for supporting oxidative formic-acid dehydrogenation to form CO2 instead of CO. However, most of Pd based catalysts feature substantially poorer durability in comparison with Pt based ones. Therefore, in order to tune the electronic surface structure of feasible alloy catalysts and obtain better overall performance, some research groups resorted to the investigation of tri-metallic catalysts like Pd-Cu-Co, Pt-Au-Ru, Pt-Pd-Cu, and Pt-Au-Cu with tunable composition.Inspired by the recent developments of de-alloying in ternary systems, we report herein on the synthesis, characterization and testing of a nanoporous (np) Au-Cu-Pt alloy catalyst with ultralow-Pt loading. Our catalyst has been synthesized by a two-step process including Cu de-alloying from previously co-electrodeposited Au0.27Cu0.70Pt0.03 alloy. As-synthesized np Au-Cu-Pt catalysts have been assessed for overall surface area by Pb underpotential deposition (PbUPD), and for Pt surface content using HUPD paralleled with CO stripping work. Scanning electron microscopy has been employed to image the morphology of as-synthesized and catalytically tested np Au-Cu-Pt films. Energy dispersive spectroscopy has been applied to confirm the synthesized alloy's atomic composition before and after catalytic testing. FAO tests have been conducted by cyclic voltammetry (CV) and chronoamperometry (CA). The CV testing provides information about the mass activity of the alloy catalyst, its overall propensity to CO poisoning and passivation with cycling. The durability of np Au-Cu-Pt catalysts has been assessed by long-term experiments including CA at constant potential (CP) and harsh potential cycling.In the main body of this talk we discuss in detail activity tests showing excellent catalytic performance of prepared catalysts manifested by more than 200 times higher mass activity than commercial Pt/GC counterparts along with remarkable durability in both harsh CV cycling and constant potential (CP) long-term tests. An unique, no-passivation cycling behavior retained for up to either 60 harsh CV cycles or 12 hours of CP testing indicates that our np Au-Cu-Pt catalysts exhibit outstanding CO-poisoning tolerance as well as unseen to date resistance to anodic passivation. Results from the testing runs have been compared critically with best performing Pt and binary Pt-alloy counterpart catalysts. The optimal electronic structure, high surface-to-volume ratio, synergistic effects, ensemble effects, strain effects, and d-band center shift are deemed responsible for the outstanding catalytic properties of the np Au-Cu-Pt catalyst developed in this work.

Au core stabilizes CO adsorption onto Pd leading to CO2 production

Au core and Pd shell supported on carbon structure Au@Pd/C can cleave the C–C bond of ethanol molecules leading to the production of a relatively high amount of CO2 when compared with Pd/C electrocatalyst as the attenuated total reflectance - Fourier transform infrared (ATR-FTIR) experiment shows. Density functional theory (DFT) calculations showed that this could be explained by the oxidation of CO species adsorbed into Pd sites that has a modified electronic structure compared with Pd/C. In terms of DFT analysis, the highest thermodynamical stability of CO in Pd shell with Au core atoms, when compared with Pd/C is because of the increase of virtual orbital states near Fermi level that can be occupied by valence electrons of CO molecule. The d-band center shift is experimentally verified using the valence band X-ray photoelectron spectroscopy and theoretically predicted by the Generalized Koopmans’ Theorem. Besides that, Au@Pd/C electrocatalyst has a better electrochemical activity when compared with Pd/C.

A-site deficient/excessive effects of LaMnO3 perovskite as bifunctional oxygen catalyst for zinc-air batteries

Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiometry can yield the positive effects on the catalytic activity of the ABO3 perovskite toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Whereas, the universality of the deficient or excessive effects and their resulting improving mechanisms on ABO3 perovskite are still ambiguous and need to be clarified. In this work, the simplest Mn-based perovskite (LaMnO3) is selected to elucidate the deficient/excessive effects and improving mechanisms on both ORR and OER. We find that A-site deficient stoichiometry is favor to the catalytic activity and stability of LaMnO3 toward both ORR and OER, whereas A-site excessive stoichiometry is deleterious to the oxygen catalytic activity and stability of LaMnO3. The high oxygen catalytic activity of La0·9MnO3 (La90) with A-site deficiency toward ORR and OER can be related to its proper Mn cation valence, large amount of oxygen vacancies, upper shift of d-band center and strong adsorption capacity to oxygenated species. The results of this work highlight the A-site deficient Mn-based perovskite as the high efficient and commercially viable bifunctional catalyst for aqueous and solid-state flexible zinc-air battery (ZAB) applications.