Center Of Pd Research Articles

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Modulating the Bader Charge Transfer in Single p‐Block Atoms Doped Pd Metallene for Enhanced Oxygen Reduction Electrocatalysis

AbstractMetallene is considered as an emerging family of electrocatalysts due to its atomically layered structure and unique surface stress. Here we propose a strategy to modulate the Bader charge transfer (BCT) between Pd surface and oxygenated intermediates via p‐d electronic interaction by introducing single‐atom p‐block metal (M=In, Sn, Pb, Bi) into Pd metallene nanosheets towards efficient oxygen reduction reaction (ORR). X‐ray absorption and photoelectron spectroscopy suggests that doping p‐block metals could facilitate electron transfer to Pd sites and thus downshift the d‐band center of Pd and weaken the adsorption energy of O intermediates. Among them, the developed Bi−Pd metallene shows extraordinarily high ORR mass activity of 11.34 A mgPd−1 and 0.86 A mgPd−1 at 0.9 V and 0.95 V in alkaline solution, respectively, representing the best Pd‐based ORR electrocatalysts ever reported. In the cathode of a Zinc‐air battery, Bi−Pd metallene could achieve an open‐circuit voltage of 1.546 V and keep stable for 760 h at 10 mA cm−2. Theoretical calculations suggest that the BCT between Pd surface and *OO intermediates greatly affects the bond length between them (dPd‐*OO) and Bi doping could appropriately reduce the amount of BCT and stretch the dPd‐*OO, thus enhancing the ORR activity.

Modulating the electronic structure of PdCoP nanonetworks alloy for efficient electro-catalysis of methanol oxidation

Modulating the d-orbital electronic structure of active metals by doping heteroatoms is efficient for the electro-catalysis of methanol oxidation reaction (MOR). However, precise doping hybrid atoms into the lattices of alloy catalysts remains challenging. Herein, the selected doping of electron-rich P atoms at the active site of Pd was achieved by hydrothermal reduction. We found that P atoms prefer to bond Pd atoms, thus tuning the electronic structure of active sites in PdCoP alloy. Consequently, the tailored PdCoP catalyst exhibited remarkable mass activity of 2.13 A mgPd−1 towards MOR, which surpasses most reported Pd-based alloy nanocatalysts. Theoretical calculations revealed that the tailored d-band center of Pd in PdCoP catalyst exhibited moderate adsorption of CO and OH intermediates, thus maximizing the MOR performance. The current work highlights the fabrication of P-doped Pd-based catalysts for realizing high MOR, which can be further extended to other energy-related applications.

A novel redox synergistic mechanism of peroxymonosulfate activation using Pd-Fe3O4 for ultra-fast chlorinated hydrocarbon degradation

Peroxymonosulfate (PMS)-based heterogeneous advanced oxidation processes for chlorinated hydrocarbons (CHCs) removal in groundwater face the challenge of limited degradation ability. In this work, recyclable catalysts composed of Pd and Fe3O4 nanoparticles were synthesized to activate PMS and generate oxidative HO• and SO4•− and reductive H•, simultaneously. The synergistic attack of different active species led to the ultra-fast degradation and mineralization of multiple CHCs. For trichloroethylene (TCE) degradation, the catalysts mass normalized reaction rate constant of Pd-Fe3O4/PMS system (30.85 L g−1 min−1) was one order of magnitude higher than reported PMS activation systems. The d-band center of Pd in Pd-Fe3O4 was close to the Fermi level, indicating that Pd(0) sites of Pd-Fe3O4 was more conducive to the activation of PMS. In addition, PMS attached Fe3O4 sites caused internal electron transfer to Pd(0) for H• generation. Higher than 97 % of CHCs removal efficiency in continuous flow experiment demonstrated the application potential of Pd-Fe3O4/PMS system.

Electron Bridge Effect Induced by Oxygen‐Bridged Ga on PdMo Bimetallene Nanoribbons for Boosting Electrocatalytic Alkynol Semihydrogenation

AbstractThe utilization of green hydrogen sources in H2O for alkynols electrocatalytic semihydrogenation reaction (ESHR) at ambient temperature provides a promising pathway toward the sustainable conversion of alkynols. However, it is still a great challenge to construct specific interfacial structure to adjust the electronic structure of Pd for the purpose of altering the strong adsorption of Pd with active hydrogen to enhance the production of alkenols. Here, the atomically dispersed GaOx‐PdMo bimetallene nanoribbons (GaOx‐PdMo BNRs) via oxygen bridging Ga atoms is designed to the surface of PdMo BNRs for 2‐methyl‐3‐butyn‐2‐ol (MBY) ESHR to the synthesis of 2‐methyl‐3‐buten‐2‐ol (MBE). The GaOx‐PdMo BNRs achieve the excellent MBE selectivity (≈97.4%), Faraday efficiency (≈96.1%), and maintain long‐term stability. Density functional theory demonstrates that the top electron‐enriched Ga atoms and the bottom electron‐deficient Pd atoms construct a “pyramidal” interface via the oxygen bridge. The unique surface can effectively activate H2O and weaken interaction between catalyst and MBE, thus promoting MBE generation. Moreover, the electron bridge effect between Ga‐O‐PdMo can induce p‐d orbital hybridization to achieve lower the d‐band center of surface Pd thus modulating the reactants adsorption. This work provides a strategy to improve ESHR performance by electron bridge effect to modulate interfacial electron distribution.

Modulating the Bader Charge Transfer in Single p-Block Atoms Doped Pd Metallene for Enhanced Oxygen Reduction Electrocatalysis.

Metallene is considered as an emerging family of electrocatalysts due to its atomically layered structure and unique surface stress. Here we propose a strategy to modulate the Bader charge transfer (BCT) between Pd surface and oxygenated intermediates via p-d electronic interaction by introducing single-atom p-block metal (M=In, Sn, Pb, Bi) into Pd metallene nanosheets towards efficient oxygen reduction reaction (ORR). X-ray absorption and photoelectron spectroscopy suggests that doping p-block metals could facilitate electron transfer to Pd sites and thus downshift the d-band center of Pd and weaken the adsorption energy of O intermediates. Among them, the developed Bi-Pd metallene shows extraordinarily high ORR mass activity of 11.34 A mgPd -1 and 0.86 A mgPd -1 at 0.9 V and 0.95 V in alkaline solution, respectively, representing the best Pd-based ORR electrocatalysts ever reported. In the cathode of a Zinc-air battery, Bi-Pd metallene could achieve an open-circuit voltage of 1.546 V and keep stable for 760 h at 10 mA cm-2. Theoretical calculations suggest that the BCT between Pd surface and *OO intermediates greatly affects the bond length between them (dPd-*OO) and Bi doping could appropriately reduce the amount of BCT and stretch the dPd-*OO, thus enhancing the ORR activity.

High-efficient electrooxidation of ethylene glycol and ethanol on PdSn alloy loaded by versatile poly(3,4-ethylenedioxythiophene)

Developing a novel catalyst with lower noble-metal loading and higher catalytic efficiency is significant for promoting the widespread application of direct alcohol fuel cells (DAFCs). In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) supported the PdSn alloy (PdSn/PEDOT) were simply synthesized and their electrocatalytic performance toward the oxidation of ethylene glycol and ethanol (EGOR and EOR) were investigated in alkaline media, respectively. In comparison with other control catalysts, the optimized Pd4Sn6/PEDOT catalyst exhibits the highest mass activity (7125/4166 mA mgPd−1) and specific activity (26/15 mA cm−2) towards EGOR/EOR. The mass activity of Pd4Sn6/PEDOT for EGOR and EOR are 11.9 and 10.9 times higher than commercial Pd/C, respectively. Moreover, chronoamperometry (CA) and successive cyclic voltammetry (CV) tests show that the CO resistance ability and durability of the Pd4Sn6/PEDOT catalyst were superior to Pd4Sn6, Pd/PEDOT and commercial Pd/C catalysts, which can be attributed to the d-band center of Pd can be effectively downshifted and the interface strain effect between electrons caused by the conjugated structure between PEDOT groups. This work provides an effective strategy for the development of highly efficient anode catalysts of DAFCs.

Modulating the d-Band Center of Palladium via Ethylene Glycol Modification: Accelerating Had Desorption for Enhanced Formate Electrooxidation.

This study addresses the critical challenge in alkaline direct formate fuel cells (DFFCs) of slow formate oxidation reaction (FOR) kinetics as a result of strong hydrogen intermediate (Had) adsorption on Pd catalysts. We developed WO3-supported Pd nanoparticles (EG-Pd/WO3) via an organic reduction method using ethylene glycol (EG), aiming to modulate the d-band center of Pd and alter Had adsorption dynamics. Cyclic voltammetry demonstrated significantly improved Had desorption kinetics in EG-Pd/WO3 catalysts. Density functional theory (DFT) calculations revealed that the presence of EG reduces the d-band center of Pd, leading to weaker Pd-H bonds and enhanced Had desorption during the FOR. This research provides a new approach to optimize catalyst efficiency in DFFCs, highlighting the potential for more effective and sustainable energy solutions through advanced material engineering.

Ru Regulated Electronic Structure of PdxCuy Nanosheets for Efficient Hydrogen Evolution Reaction in Wide pH Range.

The development of highly effective catalysts for hydrogen evolution reaction (HER) in a wide pH range is crucial for the sustainable utilization of green energy utilization, while the slow kinetic reaction rate severely hinders the progress of HER. Herein, the reaction kinetic issue is solved by adjusting the electronic structure of the Ru/PdxCuy catalysts. The champion catalyst displays a remarkable performance for HER with the ultralow overpotential (27, 28, and 97mV) in 1.0m KOH, 0.5m H2SO4, and 1.0m PBS at 10mA cm-2 and high the mass activity (3036 A g-1), respectively, superior to those of commercial Pt/C benchmarks and most of reported electrocatalysts, mainly due to its low reaction activation energy. Density functional theory (DFT) calculations indicate that Ru doping contributes an electron-deficient 3d band, which promotes water adsorption. Additionally, this also leads to an upward shift of the d-band center of Pd and a downward shift of the d-band center of Cu, further optimizing the adsorption/dissociation of H2O and H*. Results from this work may provide an insight into the design and synthesis of high-performance pH-universal HER electrocatalysts.

Optimizing the d-band center of sub-nanometer Pd–Pt alloy clusters for improved photocatalytic dehalogenation of polyhalogenated biphenyls

The efficient removal of highly toxic polyhalogenated biphenyls is rather challenging, mainly due to the difficulties in splitting C-X (X = Cl or Br) bond with high bond energy, as well as the transfer of active hydrogen species during the reduction dehalogenation process. In this work, sub-nanometer Pd–Pt alloy clusters (ca. 1 nm) supported on defect-containing TiO2(B) nanosheets (PdPt/TB), on absorption of visible light illumination (λ > 400 nm), were prepared and served as an efficient photocatalysts for dehalogenation of polyhalogenated biphenyls with H2O as the hydrogen source. An optimal sample (Pd0.7Pt0.3/TB) shows the highest photocatalytic dehalogenation efficiency for 3,3′,4,4′-trtrachlorobiphenyl (PCB77) within 30 mins, which is 12.5, 3.5 and 3 times higher than that of Pt1/TB, Pd1/TB, and Pd0.7 + Pt0.3/TB samples, respectively. Besides, 4,4′-dibromobiphenyl (PBB15) was also completely removed within 10 mins by using Pd0.7Pt0.3/TB photocatalyst, demonstrating its potential applications. Experiments and d-band theory calculations revealed that the introduction of Pt can regulate the d-band center of Pd to strength the interaction between active hydrogen with alloy and promote the transfer of hydrogen species. Meanwhile, Pd–Pt alloy is conducive to activate the C-X bond of polyhalogenated biphenyls. Finally, a mechanism based on Pd–Pt alloy clusters synergistic interaction is proposed at the molecular level. This work demonstrates the successful synthesis of sub-nanometer Pd–Pt alloy nanoclusters and elucidates the effect of interaction among Pd, Pt and supports, providing an efficient method for the removal of polyhalogenated compounds by photocatalytic technology.

Energy‐Saving Hydrogen Production by Seawater Splitting Coupled with PET Plastic Upcycling

AbstractDirect seawater electrolysis presents a promising route for grid‐scale green hydrogen (H2) production without reliance on scarce freshwater. However, it is severely hampered by high energy consumption (> 4.3–5.73 kWh m−3 H2) and harmful chlorine corrosion. Herein, an energy‐saving and chlorine‐free H2 production system by coupling seawater splitting and upcycling of polyethylene terephthalate (PET) waste into value‐added glycolic acid (GA) over a Pd─CuCo2O4 catalyst is reported. An ultra‐low potential of 1.15 V versus RHE is required to achieve an industry‐level current density of 600 mA cm−2, which reduces electricity cost to 2.45 kWh m−3 H2. Notably, this system maintains 1.6 A for longer than 100 h, demonstrating excellent stability. Experimental and theoretical results unveil that 1) the specific adsorption of PET‐derived ethylene glycol (EG) on Pd enhances the catalytic performance, and the downshifted d‐band center of Pd accelerates the desorption of GA to prevent over‐oxidation; 2) the strong adsorption of OH− on CuCo2O4 synergistically promotes EG electrooxidation (EGOR) and forms a negative charge layer that effectively repels Cl− by electrostatic repulsion, thus preventing chlorine corrosion. This work may provide new opportunities for H2 production and value‐added GA from vast marine resources and PET waste.

Acetylene Semi-Hydrogenation at Room Temperature over Pd-Zn Nanocatalyst.

A reaction of fundamental and commercial importance is acetylene semi-hydrogenation. Acetylene impurity in the ethylene feedstock used in the polyethylene industry poisons the Ziegler-Natta catalyst which adversely affects the polymer quality. Pd based catalysts are most often employed for converting acetylene into the main reactant, ethylene, however, it often involves a tradeoff between the conversion and the selectivity and generally requires high temperatures. In this work, bimetallic Pd-Zn nanoparticles capped by hexadecylamine (HDA) have been synthesized by co-digestive ripening of Pd and Zn nanoparticles and studied for semi-hydrogenation of acetylene. The catalyst showed a high selectivity of ~85 % towards ethylene with a high ethylene productivity to the tune of ~4341 μmol g-1 min-1 , at room temperature and atmospheric pressure. It also exhibited excellent stability with ethylene selectivity remaining greater than 85 % even after 70 h on stream. To the best of the authors' knowledge, this is the first report of room temperature acetylene semi-hydrogenation, with the catalyst effecting high amount of acetylene conversion to ethylene retaining excellent selectivity and stability among all the reported catalysts thus far. DFT calculations show that the disordered Pd-Zn nanocatalyst prepared by a low temperature route exhibits a change in the d-band center of Pd and Zn which in turn enhances the selectivity towards ethylene. TPD, XPS and a range of catalysis experiments provided in-depth insights into the reaction mechanism, indicating the key role of particle size, surface area, Pd-Zn interactions, and the capping agent.

Interfacial Engineering of Porous Pd/M (M = Au, Cu, Mn) Sponge-like Nanocrystals with a Clean Surface for Enhanced Alkaline Electrochemical Oxidation of Ethanol.

The interfacial engineering of Pd-based alloys (i.e., PdM with distinct morphologies, compositions, and strain defects) is an efficient way for enhanced catalytic activity; however, it remains a grand challenge to fabricate such alloys in aqueous solutions without heating, organic solvents, and multiple reaction steps. Herein, we present a simple, aqueous-phase, one-step, and ultrafast approach for the interfacial engineering of surfactant-free porous PdM (M = Cu, Au, and Mn) nanocrystals with well-controlled spongy-like morphology and compositions. The electronic interaction in PdM nanocrystals and their effect on the alkaline electrochemical ethanol oxidation reaction (EOR) are investigated using XRD, XPS, and electrochemical tests. Notably, integrating M metals into Pd atoms results in upshifting the d-band center of Pd and subsequently modulating the EOR activity and stability substantially. The EOR mass activity (10.78 A/mgPd (6.93 A/mgPdCu)) of PdCu was 1.83, 3.09, 4.51, and 53.90 times higher than those of AuPd (5.90 A/mgPd (3.27 A/mgAuPd)), PdMn (3.48 A/mgPd (3.19 A/mgPdMn)), Pd (2.39 A/mgPd), and Pd/C (0.20 A/mgPd), respectively, besides substantial durability after 1000 cycles. This is due to the porous two-dimensional morphology, a low synergetic effect, higher interfacial interaction, and greater active surface area of PdCu, besides a high Cu content with more oxophilicity that facilitates activation/dissociation of H2O to generate -OH species needed for quick EOR electrocatalysis. The electrochemical impedance spectroscopy (EIS) reveals better electrolyte/electrode interfacial interaction and lower charge transfer resistance on PdCu. The EOR activity of PdCu porous sponge-like nanocrystals was superior to all previously reported Pd-based alloys for electrochemical EOR. This study indicates that binary Pd-based catalysts with less synergetic effect are preferred for boosting the EOR activity, which could help in manipulating the surface properties of Pd-based alloys to optimize EOR performance.

Ultra-efficient electrooxidation of ethylene glycol enable by Pd-loaded Fe-doped Nb2O5 with abundant oxygen vacancies

Niobium pentoxide (Nb2O5) has emerged as a highly promising electrocatalyst for ethylene glycol oxidation reaction (EGOR) due to its eco-friendly nature and its ability to maintain structural stability in alkaline environments. However, its inherent electronic structure has posed a significant barrier to further enhancing of EGOR activity. In this study, we successfully synthesized Pd-based electrocatalysts by incorporating Fe-doped Nb2O5 with abundant oxygen vacancies (Pd/FNO-2.5), which effectively promoted ethylene glycol oxidation. The results showed that the introduction of Fe doping not only altered the electronic structure of Nb2O5, leading to the generation of oxygen vacancies, but also decreased the d-band center of Pd, thereby reducing thermodynamic energy barrier of the rate-determining step by approximately 0.58 eV. Impressively, the Pd/FNO-2.5 catalyst demonstrated remarkable electrocatalytic performance exhibiting a relatively low initial potential (−0.11 V) and high mass activity (0.380 A mg−1Pd). Furthermore, even after undergoing 100 consecutive recycling experiments, the Pd/FNO-2.5 catalyst still retained 81.10 % of its current density. This study demonstrates that doping-induced oxygen vacancy engineering is a promising approach for developing efficient EGOR electrocatalysts for direct ethylene glycol fuel cells, which is associating with the efficient and sustainable development of fuel cell and the carbon neutrality efforts.

Optimizing electronic states of Pd/WO3 nanofibers for enhanced catalytic reduction of hexavalent chromium with formic acid

Through theoretical calculations, we show that integrating Pd with WO3 nanomaterials can trigger the interfacial electron transfer from Pd to WO3, thus upshifting the d-band center (εd) of Pd to optimize toxic hexavalent chromium (Cr(VI)) reduction. The elevated εd can derive stronger chemisorption capability toward crucial formic acid molecules, notably lowering the thermodynamic energy barrier and speeding up the kinetics process. In order to realize this concept, we synthesized unique Pd/WO3 nanofibers by loading Pd nanoparticles onto electrospun WO3 nanofibers through an in situ photodeposition technique. Extensive structural, morphological, and X-ray photoelectron spectrometer (XPS) characterizations confirm the successful formation of the above nanofibers. As anticipated, the as-designed Pd/WO3 nanofibers exhibit enhanced catalytic performance in the Cr(VI) reduction with a high turnover frequency (TOF) value of 62.12 min−1, surpassing a series of reported Pd-based catalysts. Such nanofibrous WO3-induced electronic modification of Pd with a high specific area leads to catalytic enhancement, providing a novel model for catalyst design.

Modulating Pd eg orbital occupancy in Pd-Au metallic aerogels for efficient carbon dioxide reduction

The electronic structure of electrocatalysts plays a critical role in energy conversion, whereas for an efficient catalyst, it is challenging to modulate the orbitals. Herein, we present a new strategy to modulate the eg orbital occupancy of Pd by constructing composition-controllable Pd-Au metallic aerogels (MAs), optimizing the d-band center of Pd to achieve excellent performance for electrochemical carbon dioxide reduction reaction (CO2RR). Specifically, Pd1Au2 MAs achieve almost 100% Faraday efficiency (FE) of CO in the range of −0.40 to −0.80 V vs. reversible hydrogen electrode (RHE), as well as the long-term stability, being one of the best Pd-based materials for CO2RR. The X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations demonstrate that the introduction of Au modulates the Pd eg orbital occupancy, which significantly weakens *CO adsorption on Pd, reduces the CO2RR energy barrier and consequently improves the electrocatalytic activity and stability for long-term applications. Our work highlights a new strategy for designing efficient electrocatalysts for CO2RR and beyond.

Preparation of Ni@Pd Core-Shell Nanoparticles Supported on KIT-6 by Ultrasound-Assisted Galvanic Replacement for Dodecahydro-N-ethylcarbazole Dehydrogenation.

Using Ni as a template and reductant, Ni core-Pd shell nanoparticles (Ni@Pd NPs) supported on KIT-6 (Ni@Pd/K6) were prepared by a galvanic replacement reaction under ultrasonic radiation. The characterization results show that the Ni@Pd core-shell NPs with an average diameter of 1.9 ± 0.3 nm are uniformly dispersed on KIT-6. The d-band center position of Pd in Ni@Pd core-shell NPs can be affected by both ligand and strain effects. The relationship between the d-band center of Pd and the selectivity of intermediates is a nearly straight curve. The dehydrogenation efficiency of dodecahydro-N-ethylcarbazole on Ni@Pd(6:1)/K6 is 100% only for 3 h at 180 °C and 95.5% for 6 h at 160 °C, which is better than the reported catalysts. The outstanding catalytic dehydrogenation performance of Ni@Pd(6:1)/K6 can be attributed to the synergistic effect of the ligand and strain effect, the high dispersion of core-shell NPs, and the weak H2 binding ability of the catalyst.

Hetero-phase Pd4S metallene nanoribbons with Pd-rich vacancies for sulfur ion degradation-assisted hydrogen production

Vacancy defects and crystal-phase are essential parameters that affect surface electronic structure. It is still a great challenge to introduce both vacancy defects and unconventional crystal-phase into electrocatalysts to investigate their effects on the electrocatalytic performance. Herein, we in-situ constructed ultrathin Pd4S metallene nanoribbon with Pd-rich vacancies (VPd-Pd4S MNRs) via hydrothermal sulfuration for outstanding hydrogen evolution reaction (HER) and sulfion oxidation reaction (SOR) performance. Based on the metallene morphology, synergistic effect of Pd vacancies and crystal-phase, VPd-Pd4S MNRs exhibits excellent activity and long-term stability, reaching 100 mA cm−2 at 0.776 V to accomplish the simultaneous hydrogen production and sulfur ion degradation. As confirmed by density functional theory (DFT) simulations, the vacancies and S atoms affect electronic structure of catalyst surface, modulating the d-band center of Pd and thus optimizing the adsorption/dissociation during catalytic process. This work presents a promising method to simultaneously construct metal vacancies and crystal-phase in metallene electrocatalysts.

Activating the PdN4 single-atom sites for 4 electron oxygen reduction reaction via axial oxygen ligand modification

The absence of Pd ensemble sites and weak affinity for O-intermediates in tetracoordinate planar PdN4 sites inhibit O-O bond dissociation and restrict 4e- oxygen reduction reaction (ORR) pathway. Optimizing the adsorption energy between O-intermediates and PdN4 sites is a rational approach for selectively promoting 4e- ORR electrocatalysis. Herein, we propose a molten-salt strategy for introducing axial oxygen ligand into the PdN4 sites to manipulate the electronic structure and create catalytic O-PdN4 sites (one subsurface axial Pd-O configuration on PdN4 plane) on N-doped graphene nanosheets (O-PdN4-NGS). Density functional theory calculations revealed that the axial Pd-O coordination can induce charge redistribution, downshift the d-band center of Pd and enhance the adsorption affinity of PdN4 site for O-intermediates, thereby leading to superior electrocatalysis activity and selectivity for 4e- ORR process compared to conventional PdN4 sites in 0.1 M KOH (with a positive half-wave potential E1/2 of 0.90 V vs RHE). Moreover, zinc-air battery featuring with O-PdN4 sites delivers a peak power density of 178 mW cm−2 at 227.5 mA cm−2 and stable long-term cycling performance, effectively showcasing the advantages of the axial O ligand modification in practical application. This work provides a constructive strategy to activate the reaction activity and specificity of PdN4 single-atom sites by precisely-tuning the local coordination environment of Pd.

Tailored design of PdRh bimetallene nanoribbons by solvent-induced strategy for efficient alkaline hydrogen evolution

Metallene with unusual physicochemical properties is a very promising class of two-dimensional electrocatalyst for efficient electrochemical hydrogen production. However, the controllable construction of metallene in the extension direction remains a great challenge. Herein, PdRh bimetallenes (PdRh BMs) and PdRh bimetallene nanoribbons (PdRh BNRs) were controllably prepared by solvent-induced strategy for efficient hydrogen evolution. The overpotential required for PdRh BNRs to reach 10 mA cm–2 at 1 M KOH is only 32 mV, which is better than PdRh BMs and Pd metallene nanoribbons. Aberration-corrected HRTEM revealed abundant defects on the surface of PdRh BNRs, which not only act as high active sites but also generate strong strain to significantly reduce the d-band center of Pd. This work provides guidance for the construction of high efficiency catalysts in metallene by applying defect engineering and strain engineering, and also provides a novel strategy for the controllable extension of metallene in longitudinal dimension.