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The catalytic conversion of CO2 into valuable commodities has the potential to balance ongoing energy and environmental issues. To this end, the reverse water–gas shift (RWGS) reaction is a key process that converts CO2 into CO for various industrial processes. However, the competitive CO2 methanation reaction severely limits the CO production yield; therefore, a highly CO-selective catalyst is needed. To address this issue, we have developed a bimetallic nanocatalyst comprising Pd nanoparticles on the cobalt oxide support (denoted as CoPd) via a wet chemical reduction method. Furthermore, the as-prepared CoPd nanocatalyst was exposed to sub-millisecond laser irradiation with per-pulse energies of 1 mJ (denoted as CoPd-1) and 10 mJ (denoted as CoPd-10) for a fixed duration of 10 s to optimize the catalytic activity and selectivity. For the optimum case, the CoPd-10 nanocatalyst exhibited the highest CO production yield of ∼1667 μmol g−1catalyst, with a CO selectivity of ∼88% at a temperature of 573 K, which is a 41% improvement over pristine CoPd (~976 μmol g−1catalyst). The in-depth analysis of structural characterizations along with gas chromatography (GC) and electrochemical analysis suggested that such a high catalytic activity and selectivity of the CoPd-10 nanocatalyst originated from the sub-millisecond laser-irradiation-assisted facile surface restructure of cobalt oxide supported Pd nanoparticles, where atomic CoOx species were observed in the defect sites of the Pd nanoparticles. Such an atomic manipulation led to the formation of heteroatomic reaction sites, where atomic CoOx species and adjacent Pd domains, respectively, promoted the CO2 activation and H2 splitting steps. In addition, the cobalt oxide support helped to donate electrons to Pd, thereby enhancing its ability of H2 splitting. These results provide a strong foundation to use sub-millisecond laser irradiation for catalytic applications.

The composition and configuration are the deciding factors for catalytic properties and are constrained by the physical nature of the selected elements, thereby influencing the functionality of heterogeneous catalysts. In view of this, herein, a one-dimensional bifunctional heterogeneous nanocatalyst consisting of SnO2 capped Pt nanorods (Pt–SnOx NRs) is developed via the formic acid reduction method (FAM), showing high oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) performance. The performance of the as-prepared Pt–SnOx NRs was 1.4-fold higher than that of the commercial J.M.-Pt/C catalyst with an outstanding mass activity (MA) of 160 mA mgPt−1 at 0.85 V vs. SHE towards the ORR in acidic medium. Of special relevance, these Pt–SnOx NRs exhibit notable stability and retained 87% of their initial MA when operated up to 5k cycles in an accelerated durability test (ADT) in the ORR. Moreover, the Pt–SnOx NRs achieved a remarkably lower overpotential (η) of 48 mV (at a current density of 10 mA cm−2) and a Tafel slope of 33 mV dec −1 in the HER, significantly lower than those of the commercial J.M.-Pt/C catalyst (η = 60 mV and Tafel slope = 38 mV dec−1). Besides, such a material maintained its 100% HER activity in a chronoamperometric (CA) stability test up to 6 h. By cross-referencing the results of structural and electrochemical inspections, such a high bifunctional performance of Pt–SnOx NRs is attributed to the synergistic collaboration between the SnO2 modifier and Pt atoms. The SnO2 accelerates the HO–H bond cleavage during the HER and simultaneously promotes the desorption of oxygen species on the Pt surface in the ORR, which later triggers the reduction reaction performance. Meanwhile, SnO2 provides a shielding effect to Pt under harsh reduction conditions and thus high stability of Pt–SnOx NRs is achieved.

The development of electrocatalysts with reconcilable balance between the cost and performance in oxygen reduction reaction (ORR) is an imperative task for the widespread adoption of fuel cell technology. In this study, we proposed a unique model of diatomic Pt-cluster (Pt-dimer) in the topmost layer of the Co/Pd bimetallic slab (Co@Pd-Pt2) for mimicking the Cocore@Pdshell nanocatalysts (NCs) surface and systematically investigating its local-regional collaboration pathways in ORR by density functional theory (DFT). The results demonstrate that the Pt-dimer produces local differentiation from both ligand and geometric effects on the Co@Pd surface, which forms adsorption energy (Eads) gradients for relocating the ORR-adsorbates. Our calculations for Eads-variations of ORR-species, reaction coordinates, and intraparticle charge injection propose and confirm a novel local synergetic collaboration around the Pt-dimer in the Co@Pd-Pt2 system with the best-performing ORR behavior compared with all reference models. With proper selection of the composition in intraparticle components, the proposed DFT assessments could be adopted for developing economical and high-performance catalysts in various heterogeneous reactions.

The abnormal lattice expansion of commercial polypropylene (PP)/polyethylene (PE)/polypropylene (PP) separator in lithium-ion battery under different charging current densities was observed by in-situ X-ray diffraction. Significant lattice changes of both PP and PE were found during the low current density charging. The capacity fading and the resistance value of the cell measured at 0.025 C (5th retention, 92%) is unexpectedly larger than that at 1.0 C (5th retention, 97.3%) from the electrochemical impedance spectroscopic data. High-resolution scanning electron microscopy is employed to witness the pore changes of the trilayered membrane. Density functional theory calculations were used to investigate the mechanism responsible for the irregular results. The calculations revealed that the insertion of Li-ion and EC molecule into PP or PE are thermodynamically favourable process which might explain the anomalous significant lattice expansion during the low current density charging. Therefore, designing a new separator material with a more compact crystalline structure or surface modification to reduce the Li insertion during the battery operation is desirable.

The design of highly efficient, low-cost and long-term stable electrocatalysts for the hydrogen evolution reaction (HER) is a research hotspot in the field of sustainable energies (e.g., fuel cells). In this study, a novel catalyst design comprising NiO2 supported Pd nanocatalysts (NCs) with an interfacial atomic cluster of Ni metal is proposed and their HER activity with the corresponding reaction mechanism is systematically investigated by using density functional theory (DFT) calculations. For the optimum case with four Ni atoms in a tetragonal shape (i.e., NiO2–Ni4–Pd), the reaction coordinate (barrier) is reduced by 0.36 eV and 0.34 eV respectively in the Volmer and Tafel steps among models with different amounts of Ni atoms. The corresponding results reveal that the novel steric confinement effects of the atomic Ni-ensemble tetragon will unbalance the surface charge distribution to generate the local domain heterogeneity on the Pd-shell surface and further prove the doping threshold of the Ni tetragon in terms of HER-kinetics improvement. For evaluating the rationales on experimental variations by the inevitable interatomic intermix in a rapid crystal growth process, the results of various atomic doping ratios of Nid/Pd from ∼2% to 67% are systematically investigated. The adsorption energy of H* is even lower than that on Pt by further increasing Ni atoms to 32, therefore, showing the potential capability of such a type of structure design for catalysts in the HER. Based on the presented results, we believe that our research can be applied to guide the adjustment of heterogeneous catalysts in the experimental synthesis while offering a theoretical insight for designing transition metal oxide-based systems toward inexpensive, efficient and green initiative merits.

Hydrogen evolution reaction (HER) plays a key role in combating an ever-growing imbalance and adverse climatic issues. Thus far, Pt-based catalysts are treated as “the Holy Grail” for HER and none ...

A hierarchically structured bimetallic nanocatalyst (NC) comprising a metallic Pd-nanocluster adjacent to local tetrahedral symmetric Ni-oxide and a thin layer of tetramethyl orthosilicate (TMOS) decoration (denoted as NiOTPd-T) is synthesized by sequential control of the metal ion adsorption followed by wet chemical reduction on a carbon nanotube support. By cross-referencing the results of the physical structure inspections, in situ ambient pressure X-ray photoelectron spectroscopy, and gas chromatography-mass spectrometer analysis, we demonstrate that the NiOTPd-T gains an optimum production yield of 1905.1 mmol g−1 of CH4 which is more than 10-fold improved as compared to that of TMOS decorated Pd nanocatalysts (Pd-T) at 573 K. Such an exceptional performance is attributed to the local synergetic collaboration between CO chemisorption on Pd atoms and H2 splitting on both the Pd and Ni atoms at the interface region. Once the collaboration is triggered, the subsequent NiOT reduction increases the number of metallic Ni sites. It further facilitates the H2 splitting, therefore optimizing the CH4 production yield of NiOTPd-T. Most importantly, to the best of our knowledge, with such a unique Pd-to-NiOT epitaxial structure, the NiOTPd-T catalysts exhibit the highest CH4 production yield among existing catalysts with the same loading and composition and of any geometric configuration.

The rational design and synthesis of heterogeneous interfaces with tailored structural and functional properties are highly sought to realize green energy technologies. In the present study, quaternary metallic heterogeneous nanocatalysts (NCs) consisting of Pt-cluster decorated CoO2–SnPd2–SnO2 hierarchical structures (namely CSPP) are proposed with improved heteroatomic interactions for an oxygen reduction reaction (ORR) in alkaline medium (0.1 M KOH). The CSPP NCs have been synthesized with different Pt contents (1, 2 and 14 wt%) by using a wet chemical reduction method on a carbon nanotube (CNT) support with simultaneous heterogeneous and homogenous nucleation. Of special relevance, the mass activity (MA) of CSPP-1 (∼1.0 wt% Pt) and CSPP-2 (∼2.0 wt% Pt) NCs is 2146.2 mA mg−1 and 1555.7 mA mg−1, which is ∼32 and ∼23-fold increased, respectively, as compared to that of the commercial J.M.-Pt/C catalyst (20 wt% Pt) at 0.85 V vs. RHE. Through intensive analysis of microscopy and spectroscopy results, we demonstrated that such enhanced ORR activities for the ultra-low dosage of Pt are mainly dominated by incorporation of Pt atoms into the defect sites of the Co–Sn–Pd surface. These Pt-atoms lower the adsorption strength for oxygenated species via electron confinement from adjacent sites, resulting in enhanced splitting and relocation kinetics of subsequent oxygen molecules on the NC surface and thus ORR performance.

The alteration of surface functional properties via incorporation of foreign atoms is supposed to be a key strategy for the enhanced catalytic performance of noble-metal based nanocatalysts (NCs). In the present study, carbon-supported palladium (Pd)-based NCs including Pd, PdPt and PdRuPt have been prepared via a polyol reduction method under the same reduction conditions as for formic acid oxidation reaction (FAOR) applications. By cross-referencing the results of the microscopic, spectroscopic and electrochemical analysis we demonstrated that adding a small amount of platinum (Pt) into Pd NCs (i.e. PdPt NCs) significantly promotes the FAOR performance as compared to that of Pd NCs via weakening the COads bond strength at a lower voltage (0.875 V vs. NHE) than Pd (0.891 V vs. NHE). Of special relevance, the PdPt NC shows a mass activity (MA) of 1.0 A mg−1 and 1.9 A mg−1, respectively, in the anodic and cathodic scan. These values are ∼1.7-fold (0.6 A mg−1) and ∼4.8-fold (0.4 A mg−1) higher than those of Pd NC. Moreover, PdPt NC retains a higher MA (54 mA mg−1) than that of Pd NC (9 mA mg−1) after chronoamperometric (CA) stability tests over 2000 s. Meanwhile, further addition of ruthenium (Ru) (i.e. PdRuPt NCs) outstandingly enhances the CO tolerance during the CA test via removal of adsorbed COads and thus shows the highest MA (62 mA mg−1) after CA testing, which is higher than that of PdPt (54 mA mg−1) and Pd (9 mA mg−1) NCs. The intriguing results obtained in this study have great significance to provide further strategic opportunities for tuning the surface electronic properties of Pd-based NCs to design Pd-based NCs with improved electrochemical performance.

Reducing noble-metal loading and improving the oxygen reduction reaction (ORR) performance are two of the most important topics in developing a cost-effective fuel cell system. In this study, nanocatalysts (NCs) comprising NiOx supported Pd nano-islands and a sub-nanometer Pt cluster mask (NPP) are developed. We demonstrate that the oxide structure can be suppressed along with the increase of Ni intermixed by decorating with an appropriate amount of Pt cluster mask on the surface, thus boosting the ORR performance of NPP NCs. In the optimum case, with a Pt loading of 9 wt%, the Pt decorated Ni@Pd NC showed an increase in mass activity of ∼22.74-fold (1523.7 mA mg−1) and ∼26.8-fold (671.5 mA mg−1), compared to that of the commercial Pt catalyst at 0.85 volt (vs. RHE) (67.1 mA mg−1) and 0.90 volt (vs. RHE) (24.5 mA mg−1), respectively. Such an optimization can be attributed to the proper control of the surface coverage and size of the Pt clusters. This protects the surface from oxidation, thus leaving a high density of reaction sites for oxygen adsorption in the ORR. Further increasing the Pt content results in a high density of nucleation sites and a high extent of homoatomic clustering of the Pt atoms on the NiOx@Pd surface. Such a scenario reduces the surface coverage of Pt clusters and, in this event, suppresses the ORR activity of NPP NCs. The result obtained in this study is very exciting and is an important clue for the development of next-generation ORR catalysts.

Efficient generation of hydrogen from water is a key enabling technology towards alternative power generation sources. In this context, search for highly active and low-cost nanocatalysts (NCs) for the hydrogen evolution reaction (HER) is a crucial endeavour. In the present study, bimetallic NiPd with a novel epitaxial structure of tetrahedral symmetric Ni oxide (NiOT) to metallic Pd contact (denoted as NiPd-CNT) has been fabricated on a carbon nanotube (CNT) support via a wet chemical reduction method to boost HER kinetics in an acidic medium (0.5 M H2SO4). This unique structure exhibits superior catalytic activity towards the HER with a significantly lower overpotential of 46 mV (at a current density of 10 mA cm−2). Moreover, the NiPd-CNT NC showed a low Tafel slope of 38.0 mV dec−1. The overpotential and Tafel slope values are 50 mV and 22.18 mV dec−1 lower, respectively, as compared to those of the standard Pd-CNT NC and very close to the those of the commercial J.M.-Pt/C (30 wt% Pt) NC (overpotential is 44 mV@10 mA cm−2 and the Tafel slope is 30.2 mV dec−1). Of special relevance, the as-prepared NiPd-CNT NC exhibits nearly ∼95% stability when operated for 1000 cycles. Such a competitive HER performance is attributed to the formation of active sites on the catalyst surface due to strong lattice mismatch and electronegativity difference (χPd > χNi) at the heterogonous binary interface of NiO2 and Pd nanocrystals. In light of the competitive activity as compared to that of commercial J.M.-Pt/C with low cost, Pd-based bimetallic NCs can serve as a promising alternative to Pt for seizing the market.

A novel nanocatalyst (NC) with an epitaxial structure of Ni oxide adjacent to a metallic Pd nanocrystal is developed for oxygen reduction reaction (ORR). We demonstrate that, by formation of an ord...

A facile strategy for preparing carbon-supported Co95Pt5 nanocatalysts (NCs) with low platinum (Pt) loading and high Pt utilization via thermal reduction treatment in a carbon monoxide (CO) atmosphere is reported. By cross-referencing results of microscopy, X-ray spectroscopy, and electrochemical analysis, we demonstrate that the Pt atoms tend to form disordered atomic clusters capping on the Co nanoparticle surface. The values of unfilled d-states (hTs) extracted from X-ray absorption near-edge spectroscopy were used to calculate the d-band vacancies of Pt. Accordingly, CoPt-CO570 (reduced in CO at 570 K) possesses the lowest hTs value (0.302) (i.e., the lowest Pt d-band vacancies) among experimental samples, indicating a strong electron relocation from Co atoms. Such electron relocations are attributed to the high extent of the heteroatomic intermix between Pt and Co atoms and thus improves the oxygen reduction reaction activity of CoPt-CO570. For providing further evidence, structural and electrochemic...

Surface tailoring as well as inner structure design at the atomic scale are of primary importance for the activity and durability of nanocatalysts (NCs) in electrochemical applications. In this study, a novel structural candidate containing a Cu core and Pt cluster decorated Pd shell with a balance struck between the performance and cost considerations for the oxygen reduction reaction (ORR) is proposed. The carbon nanotube supported NCs are synthesized using a wet chemical reduction method with different ratios of Pt from 5 to 14 wt%. Our results demonstrate a robust assessment for programming the ORR performance by Pt loading control in the NCs. For the optimum case (∼5.0 wt% of Pt), the mass activity (M.A.) is ∼639 mA mgPt−1. This value is improved by 9-folds compared to that of commercial Pt NC (J.M.-Pt/C) at 0.85 V vs. RHE and can be attributed to the formation of a high density of surface truncations in the NC surface. When the Pt loading is ∼9 wt%, the NC forms multi-faceted twin particles with low surface defects and thus has the highest stability (+/− 0.5% of current vibration) in an accelerated degradation test (ADT) among the experimental samples. Further increasing Pt to 14 wt%, restructures the NC into a local ordered crystal with certain amounts of Pt island clusters in the surface. Such a phenomenon results in a vibration of the current density by surface restructure upon oxidation and reduction of Pt oxides in a ADT test and possesses a residual current density of 92% compared to its original value after 40 k cycles. Most importantly, our observations bring fundamental and practical insights into the role of surface defects in electrocatalysis and present a new strategy to surmount a dilemma between the reliability and activity of ORR NCs.

Hierarchical structures in shell with transition metal underneath is a promising design for high-performance and low-cost heterogeneous nanocatalysts (NCs). Such a design enables the optimum extent of synergetic effects in NC surface. It facilitates intermediate reaction steps and, therefore, boosts activity of NC in oxygen reduction reaction (ORR). In this study, carbon nanotube (CNT)-supported ternary metallic NC comprising Cucluster-in-Pdcluster nanocrystal and surface decoration of atomic Pt clusters (14 wt %) is synthesized by using the wet chemical reduction method with sequence and reaction time controls. By annealing in H2 environment (H2/N2 = 9:1, 10 sccm) at 600 K for 2 h, specific activity of Cu@Pd/Pt is substantially improved by ∼2.0-fold as compared to that of the pristine sample and commercial Pt catalysts. By cross-referencing results of electron microscopic, X-ray spectroscopic, and electrochemical analyses, we demonstrated that reduction annealing turns ternary NC into complex of Cu3Pt al...

Formic acid oxidation reaction (FAOR) at anode counterpart incurs at substantial high overpotential, limiting the power output efficiency of direct formic acid fuel cells (DFAFCs). Despite intense research, the lack of high-performance nanocatalysts (NCs) for FAOR remains a challenge in realizing DFAFC technologies. To surmount the overpotential losses, it is desirable to have NCs to trigger the FAOR as close to the reversible conditions (i.e. with over-potential loss as close to zero as possible). Herein, Pd-based binary and ternary NCs consisting of PdPt and PdRuPt have been synthesized via the polyol reduction method on the carbon support. As prepared PdPt and PdRuPt NCs were further subjected to heat treatment (annealed) in CO (namely PdPt-CO and PdRuPt-CO) and O2 (namely PdPt-O2 and PdRuPt-O2) atmosphere at 473 K temperature. By cross-referencing results of electron microscopy and X-ray spectroscopy together with electrochemical analysis, the effects of heat treatment under CO-reductive and O2-oxidative conditions towards FAOR were schematically elucidated. Of special relevance, the mass activity (MA) of PdPt-CO, PdPt-O2, PdRuPt-CO, and PdRuPt-O2 NCs is 1.7/2.0, 1.3/2.2, 1.1/5.5, and 0.9/4.7 Amg−1 in the anodic/cathodic scan, respectively, which is 2~4-folds improved comparative to of as-prepared PdPt (1.0/1.9 Amg−1 in anodic/cathodic scan, respectively) and PdRuPt (0.9/1.4 Amg−1 in anodic/cathodic scan, respectively) NCs. Meanwhile, after chronoamperometric (CA) stability test up to 2000 s, PdPt-CO (72 mAmg−1) and PdRuPt-CO (213 mAmg−1) NCs exhibit higher MA compared to as-prepared PdPt (54 mAmg−1) and PdRuPt (62 mAmg−1) NCs, which is attributed to the increase of surface Pt composition, especially for PdRuPt-CO NC. Besides, the stability of PdPt-O2 (15 mAmg−1) and PdRuPt-O2 (22 mAmg−1) NCs is deteriorated as compared to that of as-prepared NCs due to severe oxidation in O2 atmosphere. Of utmost importance, we developed a ternary PdRuPt catalyst with ultra-low Pt content (~2 wt.%) and significantly improved FAOR performance than pure Pt catalysts. Moreover, we demonstrated that the FAOR performance can be further enhanced by more than 30% via a unique CO annealing treatment.

The alteration of surface functional properties

Carbon nanotube supported ternary metallic nanocatalysts (NCs) comprising Nicore-Pdshell structure and Pt atomic scale clusters in shell (namely, Ni@Pd/Pt) are synthesized by using wet chemical reduction method with reaction time control. Effects of Pt4+ adsorption time and Pt/Pd composition ratios on atomic structure with respect to electrochemical performances of experimental NCs are systematically investigated. By cross-referencing results of high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption, density functional theoretical calculations, and electrochemical analysis, we demonstrate that oxygen reduction reaction (ORR) activity is dominated by depth and distribution of Pt clusters in a Ni@Pd/Pt NC. For the optimum case (Pt4+ adsorption time = 2 h), specific activity of Ni@Pd/Pt is 0.732 mA cm-2 in ORR. Such a value is 2.8-fold higher as compared to that of commercial J.M.-Pt/C at 0.85 V (vs reversible hydrogen electrode). Such improvement is attributed to the protection of defect sites from oxide reaction in the presence of Pt clusters in NC surface. When adsorption time is 10 s, Pt clusters tends to adsorb in the Ni@Pd surface. A substantially increased galvanic replacement between Pt4+ ion and Pd/Ni metal is found to result in the formation of Ni@Pd shell with Pt cluster in the interface when adsorption time is 24 h. Both structures increase the surface defect density and delocalize charge density around Pt clusters, thereby suppressing the ORR activity of Ni@Pd/Pt NCs.

Correction for ‘Local synergetic collaboration between Pd and local tetrahedral symmetric Ni oxide enables ultra-high-performance CO2 thermal methanation’ by Che Yan et al., J. Mater. Chem. A, 2020, 8, 12744–12756, DOI: 10.1039/D0TA02957B.

Herein, ternary metallic nanocatalysts (NCs) consisting of Au clusters decorated with a Pt shell and a Ni oxide core underneath (called NPA) on carbon nanotube (CNT) support were synthesized by combining adsorption, precipitation, and chemical reduction methods. By a retrospective investigation of the physical structure and electrochemical results, we elucidated the effects of Pt/Ni ratios (0.4 and 1.0) and Au contents (2 and 9 wt.%) on the nanostructure and corresponding oxygen reduction reaction (ORR) activity of the NPA NCs. We found that the ORR activity of NPA NCs was mainly dominated by the Pt-shell thickness which regulated the depth and size of the surface decorated with Au clusters. In the optimal case, NPA-1004006 (with a Pt/Ni of 0.4 and Au of ~2 wt.%) showed a kinetic current (JK) of 75.02 mA cm&minus, 2 which was nearly 17-times better than that (4.37 mA cm&minus, 2) of the commercial Johnson Matthey-Pt/C (20 wt.% Pt) catalyst at 0.85 V vs. the reference hydrogen electrode. Such a high JK value resulted in substantial improvements in both the specific activity (by ~53-fold) and mass activity (by nearly 10-fold) in the same benchmark target. Those scenarios rationalize that ORR activity can be substantially improved by a syngeneic effect at heterogeneous interfaces among nanometer-sized NiOx, Pt, and Au clusters on the NC surface.

With proper conjunctions between inter/intra-particle domains, the activity and durability of heterogeneous nanocatalysts (NCs) can be substantially improved by more than an order. In this study, tri-metallic NCs comprising an Ir-clusters decorated unconformable Pd-shell over amorphous NiOx core crystal underneath (namely NPI) are developed for oxygen reduction reaction (ORR) in alkaline medium (0.1 M KOH). Results for NPI NCs with different extents of Ir decoration (1 and 14 wt%) are compared for clarifying the configuration effects corresponding to ORR performance. For the optimum case with an Ir loading of ∼1.0 wt%, the mass activity (MA) is 2066.8 mAmg−1. This value is ∼31-folds increased as compared to that of commercial J.M.-Pt/C catalyst (20 wt% Pt) at 0.85 V vs RHE (67.1 mA mg−1). Moreover, as prepared NPI-0025 NC exhibits nearly 100% stability when operated up to 21 k accelerated degradation test (ADT) cycles. By cross-referencing results of physical structure inspections and electrochemical analysis, we reveal that such a high ORR performance could be attributed to the incorporation of Ir atoms in defect sites of Ni–Pd interfaces. These Ir atoms facilitate the O2 splitting by electronegativity differences to the adjacent sites, therefore, improves the ORR performance of NPI NCs.

The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) both are key electrochemical reactions for enabling next generation alternative-power supply technologies. Despite great merits, both of these reactions require robust electrocatalysts for lowering the overpotential and promoting their practical applications in energy conversion and storage devices. Although, noble metal-based catalysts (especially Pt-based catalysts) are at the forefront in boosting the ORR and HER kinetics, high cost, limited availability, and poor stability in harsh redox conditions make them unfit for scalable use. To this end, various strategies including downsizing the catalyst size, reducing the noble metal, and increasing metal utilization have been adopted to appropriately balance the performance and economic issues. This mini-review presents an overview of the current state of the technological advancements in noble metal-based heterogeneous nanocatalysts (NCs) for both ORR and HER applications. More specifically, we focused on establishing the structure–performance correlation.

The development of inexpensive and highly robust nanocatalysts (NCs) to boost electrochemical hydrogen evolution reaction (HER) strengthens the implementation of several emerging sustainable-energy technologies. Herein, we proposed a novel nano-architecture consisting of a hierarchical structured Ni@Pd nanocatalyst with Pt-clusters decoration on the surface (denoted by Ni@Pd-Pt) for HER application in acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) mediums. The Ni@Pd-Pt NC is fabricated on a carbon black support via a &ldquo, self-aligned&rdquo, heterogeneous nucleation-crystal growth mechanism with 2 wt.% Pt-content. As-prepared Ni@Pd-Pt NC outperforms the standard Pt/C (30 wt.% Pt) catalyst in HER and delivers high-rate catalytic performance with an ultra-low overpotential (11.5 mV) at the cathodic current density of 10 mA∙cm&minus, 2 in alkaline medium, which is 161.5 mV and 14.5 mV less compared to Ni@Pd (173 mV) and standard Pt/C (26 mV) catalysts, respectively. Moreover, Ni@Pd-Pt NC achieves an exactly similar Tafel slope (42 mV∙dec&minus, 1) to standard Pt/C, which is 114 mV∙dec&minus, 1 lesser when compared to Ni@Pd NC. Besides, Ni@Pd-Pt NC exhibits an overpotential value of 37 mV at the current density of 10 mA cm&minus, 2 in acidic medium, which is competitive to standard Pt/C catalyst. By utilizing physical characterizations and electrochemical analysis, we demonstrated that such an aggressive HER activity is dominated by the increased selectivity during HER due to the reduced competition between intermediate products on the non-homogeneous NC surface. This phenomenon can be rationalized by electron localization owing to the electronegative difference (&chi, Pt &gt, &chi, Pd &gt, Ni) and strong lattice mismatch at the Ni@Pd heterogeneous binary interfaces. We believe that the obtained results will significantly provide a facile design strategy to develop next-generation heterogenous NCs for HER and related green-energy applications

Hierarchical structures in shell with transition metal underneath is a promising design for high-performance and low-cost heterogeneous nanocatalysts (NCs). Such a design enables the optimum extent of synergetic effects in NC surface. It facilitates intermediate reaction steps and, therefore, boosts activity of NC in oxygen reduction reaction (ORR). In this study, carbon nanotube (CNT)-supported ternary metallic NC comprising Cucluster-in-Pdcluster nanocrystal and surface decoration of atomic Pt clusters (14 wt %) is synthesized by using the wet chemical reduction method with sequence and reaction time controls. By annealing in H2 environment (H2/N2 = 9:1, 10 sccm) at 600 K for 2 h, specific activity of Cu@Pd/Pt is substantially improved by ∼2.0-fold as compared to that of the pristine sample and commercial Pt catalysts. By cross-referencing results of electron microscopic, X-ray spectroscopic, and electrochemical analyses, we demonstrated that reduction annealing turns ternary NC into complex of Cu3Pt alloy and CuxPd1–x alloy. Such a transition preserves Pt and Pd in metallic phases, therefore improving the activity by ∼29% and the stability of NC in an accelerated degradation test (ADT) as compared to those of pristine Cu@Pd/Pt in 36 000 cycles at 0.85 V (vs RHE). This study presents robust H2 annealing for structure stabilization of NC and systematic characterizations for rationalization of the corresponding mechanisms. These results provide promising scenarios for facilitation of heterogeneous NC in ORR applications.

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.