The in situ etching assisted synthesis of Pt-Fe-Mn ternary alloys with high-index facets as efficient catalysts for electro-oxidation reactions

Hierarchical PtCuMnP Nanoalloy for Efficient Hydrogen Evolution and Methanol Oxidation

The higher amount of Pt usage and its poisoning in methanol oxidation reaction in acidic media is a major setback for methanol fuel cells. Herein, a promising dual application high-performance electrocatalyst has been developed for hydrogen evolution and methanol oxidation. A low Pt-content nanoalloy co-doped with Cu, Mn, and P is synthesized using a modified solvothermal process. Initially, ultrasmall ≈2.9 nm PtCuMnP nanoalloy is prepared on N-doped graphene-oxide support and subsequently, it is characterized using several analytical techniques and examined through electrochemical tests. Electrochemical results show that PtCuMnP/N-rGO has a low overpotential of 6.5 mV at 10 mA cm-2 in 0.3 m H2 SO4 and high mass activity for the hydrogen evolution reaction. For the methanol oxidation reaction, the PtCuMnP/N-rGO electrocatalyst exhibits robust performance. The mass activity of PtCuMnP/N-rGO is 6.790 mA mg-1 Pt , which is 7.43 times higher than that of commercial Pt/C (20% Pt). Moreover, in the chronoamperometry test, PtCuMnP/N-rGO shows exceptionally good stability and retains 72% of the initial current density even after 20,000 cycles. Furthermore, the PtCuMnP/N-rGO electrocatalyst exhibits outstanding performance for hydrogen evolution and methanol oxidation along with excellent anti-poisoning ability. Hence, the developed bifunctional electrocatalyst can be used efficiently for hydrogen evolution and methanol oxidation.

A high activity mesoporous Pt@KIT-6 nanocomposite for selective hydrogenation of halogenated nitroarenes in a continuous-flow microreactor

In this study, we designed a Pt@KIT-6 nanocomposite prepared by impregnating platinum nanoparticles on the nanopores of the KIT-6 mesoporous material. This Pt@KIT-6 nanocomposite was used as a catalyst in a micro fixed bed reactor (MFBR) for the continuous-flow hydrogenation of halogenated nitroarenes, which demonstrates three advantages. First, the Pt@KIT-6 nanocomposite has a stable mesoporous nanostructure, which effectively enhances the active site and hydrogen adsorption capacity. The uniformly distributed pore structure and large specific surface area were confirmed by electron microscopy and N2 physisorption, respectively. In addition, the aggregation of the loaded metal was avoided, which facilitated the maintenance of high activity and selectivity. The conversion and selectivity reached 99% within 5.0 minutes at room temperature (20 °C). Furthermore, the continuous-flow microreactor allows precise control and timely transfer of the reaction system, reducing the impact of haloid acids. The activity and selectivity of the Pt@KIT-6 nanocomposite showed virtually no degradation after 24 hours of continuous operation of the entire continuous-flow system. Overall, the Pt@KIT-6 nanocomposite showed good catalysis for the hydrogenation of halogenated nitroarenes in the continuous-flow microreactor. This work provides insights into the rational design of a highly active and selective catalyst for selective hydrogenation systems.

Rational Design of NiZnx@CuO Nanoarray Architectures for Electrocatalytic Oxidation of Methanol

Methanol oxidation reaction (MOR) in anodes is one of the significant aspects of direct methanol fuel cells (DMFCs), which also plays a critical role in achieving a carbon-neutral economy. Designing and developing efficient, cost-effective, and durable non-Pt group metal-based methanol oxidation catalysts are highly desired, but a gap still remains. Herein, we report well-defined hierarchical NiZnx@CuO nanoarray architectures as active electrocatalysts for MOR, synthesized by combining thermal oxidation treatment and magnetron sputtering deposition through a brass mesh precursor. After systematically evaluating the electrocatalytic performance of NiZnx@CuO nanoarray catalysts with different preparation conditions, we found that the NiZn1000@CuO (thermally oxidized at 500 °C for 2 h, nominal thickness of the NiZn alloy film is 1000 nm) electrode delivers a high current density of 449.3 mA cm-2 at 0.8 V for MOR in alkaline media as well as excellent operation stability (92% retention after 12 h). These outstanding MOR performances can be attributed to the hierarchical well-defined structure that can not only render abundant active sites and a synergistic effect to enhance the electrocatalytic activity but also can effectively facilitate mass and electron transport. More importantly, we found that partial Zn atoms could leach from the NiZn alloy, resulting in rough surface nanorods, which would further increase the specific surface area. These results indicate that the NiZn1000@CuO nanoarray architecture could be a promising Pt group metal alternative as an efficient, cost-effective, and durable anode catalyst for DMFCs.

Synthesis, Composition, Structure, and Electrochemical Behavior of Platinum–Ruthenium Catalysts

The bimetallic PtRu nanoparticles deposited on the carbon support with the metals’ atomic ratio of 1:1 have been obtained by different liquid-phase synthesis methods. The metals’ mass fraction in the obtained PtRu/C catalysts is about 27%. The average size of the bimetallic nanoparticles ranges from 1.9 to 3.9 nm. The activity of the obtained PtRu/C catalysts in the methanol electrooxidation reaction as well as their tolerance to intermediate products of its oxidation have been studied. The sample synthesized by the polyol method has proved to be the most active material. The values of its electrochemical surface area and activity in the methanol electrooxidation reaction are 1.5–1.7 times higher than those of the commercial PtRu/C analogue. Nevertheless, the use of the polyol method leads to losses of the metals during the synthesis. Therefore, this method needs further optimization.

Facile synthesis of low-dimensional PdPt nanocrystals for high-performance electrooxidation of C 2 alcohols

Low-dimensional noble-metal materials (LDNMs) with different structural advantages have been considered as the high-performance catalysts for C2 alcohol electrooxidation. However, it is still a great challenging to precisely construct nanomaterials with low-dimensional composite structure thus to take advantages of various dimension, especial without the surfactant participation. Most studies focus on the modulation of the single dimensional nanocatalysts, the correlation between electrocatalytic performances and low-dimension composite have been rarely reported. Herein, we engineered a simple one-step approach to design multi-low-dimensional PdPt nanomaterials by using different Pd precursors. The low-dimensional PdPt nanocrystals (NCs) composed of zero dimension (0D) dendrite-like nanoparticles and two dimension (2D) nanosheets were obtained by using Pd(OAc)₂, and meanwhile the 2D PdPt nanosheet assemblies (NAs) were synthesized by the introduction of NaPdCl₄. Specifically, benefitting from the unique low-dimension structures with fast electron/mass transfer, and optimized electronic and synergistic effect, the multi-low-dimensional 0D-2D PdPt NCs showed the highest ethanol oxidation reaction (EOR)/ethylene glycol oxidation reaction (EGOR) mass activities, which were much higher than 2D PdPt NAs. The 0D-2D PdPt NCs also exhibited the highest structural stability. Generally, this work could inspire more advanced designs for surfactant-free synthesis and promote the fundamental engineering on nanocatalysts with low-dimension composite structure for electrocatalytic fields.

Recent Advances in Carbon Dioxide Conversion: A Circular Bioeconomy Perspective

Managing the concentration of atmospheric CO2 requires a multifaceted engineering strategy, which remains a highly challenging task. Reducing atmospheric CO2 (CO2R) by converting it to value-added chemicals in a carbon neutral footprint manner must be the ultimate goal. The latest progress in CO2R through either abiotic (artificial catalysts) or biotic (natural enzymes) processes is reviewed herein. Abiotic CO2R can be conducted in the aqueous phase that usually leads to the formation of a mixture of CO, formic acid, and hydrogen. By contrast, a wide spectrum of hydrocarbon species is often observed by abiotic CO2R in the gaseous phase. On the other hand, biotic CO2R is often conducted in the aqueous phase and a wide spectrum of value-added chemicals are obtained. Key to the success of the abiotic process is understanding the surface chemistry of catalysts, which significantly governs the reactivity and selectivity of CO2R. However, in biotic CO2R, operation conditions and reactor design are crucial to reaching a neutral carbon footprint. Future research needs to look toward neutral or even negative carbon footprint CO2R processes. Having a deep insight into the scientific and technological aspect of both abiotic and biotic CO2R would advance in designing efficient catalysts and microalgae farming systems. Integrating the abiotic and biotic CO2R such as microbial fuel cells further diversifies the spectrum of CO2R.

Pt-based (Zn, Cu) nanodendrites with enhanced catalytic efficiency and durability toward methanol electro-oxidation via trace Ir-doping engineering

Pt-based alloy nanomaterials with nanodendrites (NDs) structures are efficient electrocatalysts for methanol oxidation reaction (MOR), however their durability is greatly limited by the issue of transition metals dissolution. In this work, a facile trace Ir-doping strategy was proposed to fabricate Ir-PtZn and Ir-PtCu alloy NDs catalysts in aqueous medium, which significantly improved the electrocatalytic activity and durability for MOR. The as-prepared Ir-PtZn/Cu NDs catalysts showed distinct dendrites structures with the averaged diameter of 4.1 nm, and trace Ir doping subsequently improved the utilization of Pt atoms and promoted the oxidation efficiency of methanol. The electrochemical characterizations further demonstrated that the obtained Ir-PtZn/Cu NDs possessed enhanced mass activities of nearly 1.23 and 1.28-fold higher than those of undoped PtZn and PtCu, and approximately 2.35 and 2.67-fold higher than that of Pt/C in acid medium. More excitingly, after long-term durability test, the proposed Ir-PtZn and Ir-PtCu NDs still retained about 88.9% and 91.6% of its initial mass activities, which further highlights the key role of Ir-doping in determining catalyst performance. This work suggests that trace Ir-doping engineering could be a promising way to develop advanced electrocatalysts toward MOR for direct methanol fuel cell (DMFC) applications.

Nickel nanocrystal/nitrogen-doped carbon composites as efficient and carbon monoxide-resistant electrocatalysts for methanol oxidation reactions

High-performance electrocatalysts for the methanol oxidation reaction (MOR) are the key to advance the application of direct methanol fuel cells. Pt-Based electrocatalysts for the MOR are limited due to their high cost, low stability and poor resistance to carbon monoxide (CO) poisoning. The development of non-noble metal-based electrocatalysts for the MOR with high activity and good stability is desired, but it remains a challenge. Herein, we report a simple strategy to prepare nickel nanocrystals embedded in a nitrogen-doped carbon matrix (Ni/N-C composite) by pyrolysis of Ni-coordinated polyaniline-poly(vinyl alcohol) hydrogels. These in situ generated Ni nanocrystals serve as active electrocatalysts for the MOR, while the nitrogen-doped carbon matrix serves as a conductive support to facilitate electron transfer and also to protect the active Ni nanocrystals. The optimal Ni/N-C@500 electrocatalyst shows a high MOR activity of 147 mA cm-2 at 1.66 V vs. the RHE in alkaline methanol solution, which is outstanding among Ni-based MOR electrocatalysts. Ni/N-C@500 also shows better stability than the Pt/C catalyst in the long-term MOR test at high current densities. Upon CO poisoning, Ni/N-C@500 retains 85% of its MOR activity, far exceeding the performance of the Pt/C catalyst (61% retention). Owing to its facile synthesis, outstanding activity and high stability, the Ni/N-C@500 composite is promising as a low-cost, efficient and CO-resistant electrocatalyst for the MOR.

A scalable synthesis of ternary nanocatalysts for a high-efficiency electrooxidation catalysis by microfluidics

Microfluidic synthesis has attracted extensive attention due to the ability for the multistep precise control of the synthesis parameters, continuous and reproducible preparation, and its ease of integration. However, its commercial application is still affected by its low production efficiency. In this case, we report a high-throughput continuous flow synthesis of highly dispersed PtFeCu/C nanocatalysts using a metal microchip setup with four parallel channels. The high flow rate and integrated channels enabled improving the throughput, whereby 1.33 g h^-1 of catalysts could be achieved with the flow rate of 1200 mL h^-1 under the experimental conditions. The as-prepared PtFeCu/C exhibited excellent performance, 1.94 times higher than Pt/C for methanol oxidation. More importantly, the yield of the PtFeCu/C nanocatalysts could be further increased through designing numerous parallel channels, which might provide a promising approach for large-scale commercialization of the catalysts. Such a high-throughput fabrication pathway is significant for the large-scale industrial production of nanomaterials.

CO-Reductive and O2-Oxidative Annealing Assisted Surface Restructure and Corresponding Formic Acid Oxidation Performance of PdPt and PdRuPt Nanocatalysts

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.

Achieving Superior Electrocatalytic Performance by Surface Copper Vacancy Defects during Electrochemical Etching Process

Vacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra-stable three-dimensional PtCu nanowire network (NNW) with ultrafine size, self-supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect-rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density-functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution.

Ternary PtFeCo alloys on graphene with high electrocatalytic activities for methanol oxidation

Ternary PtFeCo alloys as alternatives to conventional Pt electrocatalysts are highly important in the field of the methanol oxidation reaction. In this study, we demonstrate a one-pot two-step reduction method for the synthesis of graphene supported PtFeCo alloy nanocomposites as an integrated binder-free catalyst. The synergistic effect of alloying with Fe and Co as well as graphene decorating contributes to an increase in the utilization of the noble metal, namely, reducing the amount of Pt in the nanocomposites to 7%. After tailoring the elemental composition of the alloys, Pt₅₂Fe₂₉Co₁₉@G-7% exhibits a mass activity/specific activity of 1758.2 mA mg^-1_Pt/3.42 mA cm^-2 that is 3.13/3.45 times that of commercial Pt/C in an acidic medium. Impressively, it showed a superior mass current density of 9356.1 mA mg^-1_Pt at 60 °C which is close to the operating temperature of direct methanol fuel cells. Moreover, the as-obtained Pt₅₂Fe₂₉Co₁₉@G-7% also exhibited excellent CO tolerance and reliable stability compared to commercial Pt/C. The structural characterization further verifies that the surface strain and electronic effect play a critical role in determining the electrocatalytic properties of PtFeCo@G nanocomposites for the methanol oxidation reaction.

Self-template synthesis of defect-rich NiO nanotubes as efficient electrocatalysts for methanol oxidation reaction

Developing robust and inexpensive non-noble metal based anode electrocatalysts is highly desirable for alkaline direct methanol fuel cells (ADMFCs). Herein, we successfully develop a facile self-template synthetic strategy for gram-grade porous NiO nanotubes (NTs) by pyrolyzing a nanorod-like Ni-dimethylglyoxime complex. The pyrolysis temperature highly correlates with the morphology and crystallinity of NiO NTs. The optimal NiO NTs exhibit a large electrochemically active surface area, a fast catalytic kinetics, and a small charge transfer resistance, which induce an outstanding electrocatalytic activity for the methanol oxidation reaction (MOR). Compared with conventional NiO nanoparticles, NiO NTs achieve a 11.5-fold increase in mass activity at 1.5 V for the MOR due to nanotubal morphology and abundant non-vacancy defects on the NiO NT surface. Moreover, NiO NTs have a higher electrocatalytic activity for the intermediates of the MOR (such as formaldehyde and formate) than conventional NiO nanoparticles, which also contribute to MOR activity enhancement. Given the facile synthesis and enhanced electrocatalytic performance, NiO NTs may be promising anode electrocatalysts for ADMFCs.

Synthesis of low- and high-index faceted metal (Pt, Pd, Ru, Ir, Rh) nanoparticles for improved activity and stability in electrocatalysis

Driven by the quest for future energy solution, faceted metal nanoparticles are being pursued as the next generation electrocatalysts for renewable energy applications. Thanks to recent advancement in solution phase synthesis, different low- and high-index facets on metal nanocrystals become accessible and are tested for specific electrocatalytic reactions. This minireview summarises the key approaches to prepare nanocrystals containing the most catalytically active platinum group metals (Pt, Pd, Ru, Ir and Rh) exposed with low- and high-index facets using solution phase synthesis. Electrocatalytic studies related to the different facets are highlighted to emphasise the importance of exposing facets for catalysing these reactions, namely oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), alcohol oxidation including methanol (MOR) and ethanol oxidation reactions (EOR), formic acid oxidation reaction (FAOR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The future outlook discusses the challenges and opportunities for making electrocatalysts that are even more active and stable.

High-density surface protuberances endow ternary PtFeSn nanowires with high catalytic performance for efficient alcohol electro-oxidation

Developing cost-effective catalysts with superb activity and stability to alcohol electro-oxidation is a decisive factor towards the progress of direct alcohol fuel cells (DAFCs). Rationally utilizing the architectural and surface microstructural sensitivity of nanocatalysts can significantly increase their electrocatalytic properties. Here, we report an appropriate route that allows the fabrication of ultrafine PtFeSn nanowires (NWs) with tunable compositions. Interestingly, the addition of Sn reconstructed the surface microstructures, making ultrafine 1D NWs rich in a large number of surface protuberances, which may facilitate the oxidation of ethanol and methanol. Impressively, further catalytic studies demonstrate that all the PtFeSn NWs exhibit excellent catalytic capabilities for ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR), and display composition-related electrocatalytic activity with Pt1Fe0.20Sn0.46 NWs, possessing the highest activity for EOR and MOR. In addition, the trimetallic PtFeSn NWs exhibit significant meliorative durability relative to PtFe NWs and commercial Pt/C. The superb electrocatalytic performance is ascribed to its one-dimensional (1D) structure, atomic-level fine diameter, synergistic effect among Pt, Fe, and Sn components and abundant protuberances on the surface. Thus, this study highlights the significance of accurate structure- and surface-controlled Pt-based NWs for electrocatalysis and provides a universal approach for designing multi-component catalysts.