Precious Metal Content Research Articles

Effects of strain, pH and oxygen-deficient on catalytic performance of Ruddlesden-Popper oxide Srn+1RunO3n+1 (n=1, 2) for hydrogen evolution reaction

Due to low content of precious metals and good stability, Ruddlesden-Popper (R–P) structure oxides are considered as promising hydrogen evolution reaction (HER) catalysts. However, related research is scarce, hindering its further improvement. In this paper, effects of strain, pH, oxygen-deficient and layer numbers on HER catalytic performance of R–P structure oxides Sr2RuO4, Sr3Ru2O7 and Sr3Ru2O6 were comprehensively calculated for the first time. Our results confirm that oxygen-deficient R–P Sr3Ru2O6 is beneficial for its catalytic performance in alkaline environments. Ranking of catalytic performance in acidic environments: Sr2RuO4>Sr3Ru2O6>Sr3Ru2O7, relatively in alkaline environments: Sr3Ru2O6>Sr3Ru2O7>Sr2RuO4, which means pH actually affects the performance of R–P structure catalysts. In other words, acidic environments are conducive to the catalytic activity of Sr2RuO4, while alkaline environments are beneficial for Sr3Ru2O6 and Sr3Ru2O7. We also calculated the effects of tensile and compressive strains and found that 1% and 3% tensile strain can further enhance the HER catalytic performance of Sr3Ru2O6. Taking into account various practical factors, our work investigated the HER catalytic mechanism of R–P oxides, providing theoretical guidance for the development of R–P structure catalysts.

Enhancing Stability of Surface Au under Oxidizing Conditions through Reduced Bulk Au Content.

Contrary to the common assumption that a higher bulk content of precious metals facilitates the preservation of more surface noble metal by serving as a reservoir for surface enrichment, we demonstrate that a lower bulk content of Au results in a more stable arrangement of Au atoms at the surface of Cu-Au nanoparticles when exposed to an O2 atmosphere. Using ambient pressure X-ray photoelectron spectroscopy, we investigate the surface segregation and oxidation behavior of Cu-Au nanoparticles across various compositions. Our results reveal that in Au-rich nanoparticles exposed to an H2 atmosphere, surface segregation prompts the formation of a continuous Au-enriched shell, which subsequently oxidizes into a complete CuOx shell upon transitioning to an O2 atmosphere. Conversely, in Au-poor nanoparticles during H2 treatment, segregation results in the emergence of Au clusters embedded within the surface layer, persisting upon exposure to O2. This unexpected phenomenon shows that reducing the bulk content of precious metals can enhance the surface stability of noble atoms under oxidizing conditions, as further demonstrated by comparing the catalytic performance of Cu-Au nanoparticles with varying Au bulk contents in CO oxidation.

Metal–organic framework derived RuNiMo/NC for enhanced hydrogen production and methanol reforming electrolysis

It is important to probe the effect of doping of ultratrace content of precious metal and synergistic effects of multimetals on effective electrocatalysts for water splitting. Thus, ultratrace content Ru doping NiMo-NC were acquired through simple hydrothermal technology and high-temperature pyrolysis. Benefiting from porous structure, ultratrace content Ru doping and synergistic effect of multiple metals, RuNiMo-NC-2 presents the small overpotentials of 130 and 199 mV for MOR to achieve 10 and 100mA cm−2 in 1 mol/L potassium hydroxide with 5 mol/L methanol. The assembled water electrolyzer with the RuNiMo-NC-2||RuNiMo-NC-2 couple only requires 1.49 V to realize 10mA cm−2 for the overall water splitting in 1 mol/L potassium hydroxide with 5 M methanol. This paper offers a feasible method for designing bifunctional electrocatalysts with superior electrocatalytic performance, which can be used in hydrogen production through water electrolysis.

Regulation of surface oxygen vacancy of Cu-CeO2/TiO2 heterostructures via fast Joule heating method for enhanced CO2 electrochemical reduction

Strict control of carbon emissions is crucial for expediting the achievement of carbon neutrality. However, the current CO2RR electrocatalytic exhibits numerous shortcomings that impede the enhancement of catalytic activity. Issues such as lengthy catalyst preparation times, and high levels of precious metal content. Additionally, the aggregation of ultrafine nanoparticles contributes to a rapid deterioration in catalytic performance. Herein, a Joule-heating method is efficiently utilized to synthesize heterostructures nano-catalysts for CO2 electroreduction on carbon cloth substrates. This method takes advantage of the thermoelectric coupling of the carbon cloth to achieve carbothermal reduction, while also regulating phase composition and introduction of oxygen vacancies. The Cu-CeO2/TiO2/CC catalyst synthesized in this method showed a current density in CO2 of −32 mA·cm−2 at −1.0 V (vs. RHE). Notably, this catalyst demonstrated high CO selectivity and Faraday efficiency (FECO) of up to 82.5 % at a low potential of −0.3 V (vs. RHE). Optimal electrochemical performance is achieved at a power of 40 W. The ultra-fast temperature change process prevented the agglomeration of catalyst particles and facilitated the construction of a stable heterogeneous interface with a high oxygen vacancy concentration. In conclusion, this study presents a promising approach, particularly for the rapid preparation of low-cost, highly selective non-precious metal electrocatalysts.

Leaching of base metals in PCBs and copper cementation by iron powder

When dealing with electronic waste, printed circuit boards (PCBs) are some of the most important materials in terms of recovery possibilities, because of their high content of precious metals and base metals, notably copper (> 20% w/w), in addition to organic resins and ceramic materials. Efficient hydrometallurgical metals recovery from electronic waste is an important on-going research topic, and the present study consisted in the development of a process for the concentration of precious metals by leaching and recovery of major base metals mainly copper.A fraction of crushed PCBs concentrated in metals with more than 50 % copper was used for the leaching tests for two types of components: processor cards and mobile phone cards. For the leaching process, two steps were carried out. A first step consisted in leaching the concentrate three times with sulfuric acid and hydrogen peroxide, a second step consisted in lead removal by nitric acid leaching.The obtained results exhibit that, for processor cards, the first stage of leaching allowed the extraction of about 98 % of copper. Other base metals, zinc (99.8 %) and nickel (96 %) were also significantly leached. Precious metals were less leached except Ag with 88 % of release. The second stage of leaching with nitric acid allowed significant removal of lead (66 %). For mobile phone cards, the first stage of leaching led to an almost complete extraction of Cu (>98 %) and some other base metals (Fe, Ni, Sn, and Zn > 90 %). Al, Co and Mn were also extracted at 76 %, 78 % and 81 % respectively. Precious metals remained in the residue, except Pd which was leached at 16 %. The second stage of leaching with dilute nitric acid solution was not necessary for mobile phone cards, as it was responsible of an important Ag release from residue (80 %).

Management of the Work Environment to Reduce Blood Lead (BLL) Levels in the Assay Laboratory

Assay Laboratory in PT Freeport Indonesia's Concentrating Division, especially for conducting fire assay. Litharge (lead oxide) is a reagent used to test mineral levels; the content of precious metals is called Au. Although lead exposure is low, prolonged exposure to lead could accumulate in the human system, resulting in poisoning or toxicity. This study aimed to determine the effect of work environment management in assay laboratories on reducing blood lead levels during fire assay analysis. This research is a quantitative cohort study. The sampling technique used is purposive sampling. Data analysis techniques are used in different tests. Data collection was conducted using laboratory tests to take blood samples once a year regularly for every worker working in the assay laboratory. Based on the results of the different tests, a T value of 5,638 was obtained with a Sig value of 0.011 (α˂5%), so it can be concluded that there was a decrease in blood Pb levels in workers before and after managing the work environment. Recommended exposure standards are floor exposure values for laboratories (other than fire test laboratories) not to exceed 2.2 mg/m2 (200 μg/ft2) and surface in dining areas not to exceed 0.43 mg/m2 (40 μg/ft2). Improving working environment conditions by procuring a laundry system and lockers, procuring more than one laboratory coat, procuring sinks in every corner of the laboratory, and having special soap for washing hands has proven to be able to reduce Pb exposure rates in assay laboratories from 2019 to 2022.

Enhanced recovery of low-grade copper ore and associated precious metals from iron tailings: A case study in China

In the processing of copper and precious metal recovery in a mine in Chengde, Hebei Province, the decrease in copper mineral content and finer grain size distribution of the selected ores have caused challenges in the existing milling process. This has led to difficulties in achieving significant dissociation of chalcopyrite, resulting in decreased separation efficiency of copper and associated precious metals. Particularly, there is a notable loss of precious metals in the flotation tailings. Using BPMA and other detection equipment, the occurrence state, distribution patterns, and liberation degree of copper and associated precious metals in iron tailings were investigated. Subsequent flotation experiments examined the impact of grinding regimes on mineral liberation and reagent regimes on mineral enrichment. Subsequently, flotation experiments were conducted to examine the influence of grinding regimes on mineral liberation and reagent regimes on mineral enrichment. The research findings revealed that copper and precious metal contents in iron tailings are extremely low and finely disseminated within gangue minerals, posing challenges for liberation. Under the optimal conditions determined from flotation experiments, a laboratory closed-circuit process consisting of one rougher, one scavenger, and two cleaner stages yielded a copper concentrate with a grade of 11.33 %, a recovery efficiency of 66.95 %, and containing 9.42 g/t gold, 52.72 g/t silver, 2.78 g/t platinum, and 8.46 g/t palladium. The SEM-EDS analysis further emphasizes the necessity to tailor grinding and flotation processes to optimize the liberation and subsequent recovery of these valuable minerals, avoiding excessive grinding of gangue minerals which could negatively impact flotation performance.

Co-doped hollow nanospheres with low Pt loading for electrocatalytic oxygen reduction and zinc-air batteries

Preparing high-performance catalysts for oxygen reduction reaction (ORR) with low Pt loading is crucial to promote the development of clean energy storage devices such as metal air batteries. Herein, Co/N-HCMs support material with isolated Co atoms and hollow flower-like structure could be prepared by a self-sacrificing template strategy. Co/N-HCMs are then used to anchor Pt to obtain PtCo/N-HCMs catalyst with low Pt loading. Thanks to its improved specific surface area, hierarchical porous structure, and reinforced metal-support interactions, the obtained PtCo/N-HCMs deliver high onset potential of 0.99 V and half-wave potential of 0.82 V, and an excellent durability. When used as air cathode catalyst, PtCo/N-HCMs-based Zinc-air battery (ZAB) exhibits a power density of up to 202 mW cm−2, which is significantly better than ZAB assembled with commercial Pt/C. This study provides an effective strategy for preparing high-performance electrocatalysts with low precious metal content for use as the cathode of metal-air batteries.

An alternative classification approach for waste electronic and electrical equipment (WEEE) recovery in low-income countries: case study in Burkina Faso.

Waste electrical and electronic equipment (WEEE) is defined as "urban mines" due to the various recoverable minerals they contain. However, current WEEE classification methods are mostly limited to their physical characteristics, focusing on collection, transport, and treatment purposes rather than on valorization. In the present study, our aim is to propose an alternative classification approach adapted for low-income countries for WEEE recovery that highlights their content of precious and valuable metals. A typology of WEEE was created based on WEEE generated in Ouagadougou (Burkina Faso). Principal component analysis (PCA) and the moving center technique (K-means) were used for the classification method. Ultimately, we have found that to improve the recovery of WEEE, they can be classified into three main groups: (i) a group of WEEE-containing batteries, (ii) a group of WEEE-containing valuable and precious metals, and finally, (iii) a group of WEEE made up of cathode ray tube televisions (CRT-TV) waste. The WEEE belonging to the second group are the ones that could generate higher economical values. This alternative classification approach will help investors and operators to better orient their valorization activities towards WEEE types that present the best precious metals recovery potential, maximizing their profits. On the other hand, decision-makers will find this classification useful for reorganizing the WEEE value chain.

NEW TECHNOLOGIES FOR PROCESSING TAILINGS OF A COPPER PROCESSING PLANT FOR THE EXTRACTION OF PLATINOIDS

The most important task of the mining and metallurgical industry in the world is the development of technology for the processing of industrial waste from metallurgical industries. In the world, balance ores of precious metals are practically available. This issue develops the processing of man-made waste, refractory ores, off-balance and low-grade dumps. The article considers studies of the material and rational compositions of the tailings of a copper concentrating plant in the conditions of JSC Almalyk MMC, determines the optimal method for tailings enrichment with an increase in the content of precious metals in the concentrate, and enhances an unconventional new scheme for processing platinum group concentrates with the extraction of platinum, palladium, silver and high recovery gold. Based on the learned subjects and analysis of studies results, the authors concluded that the centrifugal concentration of platinoids from the composition of the tailings was achieved due to accurate determinations of the particle size in the tailings with the selection of intense gravity modes. Combined hydrometallurgical methods for purifying platinoids and gold from impurities using combinations of chemical solvents have been developed. As a result, the developed technologies have achieved the possibility of complex extraction of platinum group metals from the tailings of concentrating plants of copper production with high degrees, through extraction of all precious metals.

NEW TECHNOLOGIES FOR PROCESSING TAILINGS OF A COPPER PROCESSING PLANT FOR THE EXTRACTION OF PLATINOIDS

The most important task of the mining and metallurgical industry in the world is the development of technology for the processing of industrial waste from metallurgical industries. In the world, balance ores of precious metals are practically available. This issue develops the processing of man-made waste, refractory ores, off-balance and low-grade dumps. The article considers studies of the material and rational compositions of the tailings of a copper concentrating plant in the conditions of JSC Almalyk MMC, determines the optimal method for tailings enrichment with an increase in the content of precious metals in the concentrate, and enhances an unconventional new scheme for processing platinum group concentrates with the extraction of platinum, palladium, silver and high recovery gold. Based on the learned subjects and analysis of studies results, the authors concluded that the centrifugal concentration of platinoids from the composition of the tailings was achieved due to accurate determinations of the particle size in the tailings with the selection of intense gravity modes. Combined hydrometallurgical methods for purifying platinoids and gold from impurities using combinations of chemical solvents have been developed. As a result, the developed technologies have achieved the possibility of complex extraction of platinum group metals from the tailings of concentrating plants of copper production with high degrees, through extraction of all precious metals.

Exploring the synergistic effect of palladium nanoparticles and highly dispersed transition metals on carbon nitride/super-activated carbon composites for boosting electrocatalytic activity

In the present work, multifunctional electrocatalysts formed by palladium nanoparticles (Pd NPs) loaded on Fe or Cu-containing composite supports, based on carbon nitride (C3N4) and super-activated carbon with a high porosity development (SBET 3180 m2/g, VDR 1.57 cm3/g, and VT 1.65 cm3/g), were synthesised. The presence of Fe or Cu sites favoured the formation of Pd NPs with small average particle size and a very narrow size distribution, which agreed with Density Functional Theory (DFT) calculations showing that the interaction of Pd clusters with C3N4 flakes is weaker than with Cu- or Fe-C3N4 sites. The electroactivity was also dependent on the composition and, as suggested by preliminary DFT calculations, the Pd-Cu catalyst showed lower overpotential for hydrogen evolution reaction (HER) while bifunctional oxygen reduction reaction/ oxygen evolution reaction (ORR/OER) behaviour was superior in Pd-Fe sample. The Pd-Fe electrocatalyst was studied in a zinc-air battery (ZAB) for 10 h, showing a performance similar to a commercial Pt/C + RuO2 catalyst with a high content of precious metal. This study demonstrates the synergistic effect between Pd species and transition metals and shows that transition metals anchored on C3N4-based composite materials promote the electroactivity of Pd NPs in HER, ORR and OER due to the interaction between both species.

Highly selective recovery of gold and silver from E-waste via stepwise electrodeposition directly from the pregnant leaching solution enabled by the MoS2 cathode

The recycling of electronic waste, i.e., waste Printed Circuit Boards (WPCBs), provides substantial environmental and economic advantages. In fact, the concentration of valuable precious and base metals in WPCBs is even higher compared to those found in mined ores. Nevertheless, it is still challenging to selectively extract precious metals with low concentrations from the pregnant leaching solution, due to the co-deposition of base metals, like Cu, which have higher concentrations. In this research, stepwise recovery of precious metals and copper directly from WPCBs thiosulfate leaching solution was facilitated by the Ti cathode coated with MoS2 (MoS2/Ti). The in-situ enrichment of Au(S2O3)23- and Ag(S2O3)23- at the surface of MoS2 enables the high efficiency and selectivity of electrodeposition, which has been confirmed through COMSOL Multiphysics simulations and visualization. As a result, the first-step electrodeposition at 0.6 V recovered 92.44 % Au and 98.18 % Ag without any co-deposition of Cu. Subsequently, the second-step recovery employed a constant current of 0.03 A, achieving 100 % recovery of copper within 12 h. Furthermore, this study optimized the reduction potential, NH3·H2O concentration, and S2O32- concentration for the stepwise electrodeposition process. These findings provide valuable insights for establishing a closed loop circular economy in the electronics industry.

(Electrodeposition Division Research Award) New Frontiers of Electrodeposition for Metallic Finishes

The interest in scientific research within the metal finishing sector is growing. The demand for durable metals and adaptable manufacturing processes is increasing across a wide range of applications, from aerospace and automotive to machinery and jewelry. In that respect, alloy plating offers better answers in terms of economic growth and environmental sustainability due to fine-tuning composition, morphology, and crystallinity [1]. Here, current trends in alloy electrodeposition research are reviewed highlighting open challenges and process innovations from an industrial perspective. Combining basic electrochemical techniques with spectroscopic, microscopic, and structural techniques is crucial for characterizing the structure-activity relationship for many different technological devices. Particular attention is devoted to advances in industrial quality control and viable solutions for the reduction of precious metal content in electroplated accessories as well as the replacement of cyanide and nickel baths with non-toxic compounds. Project funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3 - Call for tender No. 341 of 15 March 2023 of Italian Ministry of University and Research (MUR) funded by the European Union - NextGenerationEU - Project code PE_00000004, CUP B83C22004890007, Project title "3A-ITALY - Made-in-Italy circolare e sostenibile".

Grooved Electrodes for High Power Density Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are a promising alternative to internal combustion engines, owing to their intrinsic power density, decoupled energy storage and generation, and relatively short refueling time. However, challenges related to cost, performance, and durability continue to prevent wide adoption of PEMFCs.1 Development of alternative electrode structures, which can enable smaller and less expensive PEMFCs with higher power and lower precious metal content, provides a promising path to overcome these challenges.2 Here, we report grooved electrodes, where the transport pathways of H+ and O2 were partitioned. Specifically, H+ are transported through electrode ridges with optimized ionomer content, and O2 is transported through the grooves that separate the electrode ridges. The grooved electrodes made with commercial electrode materials enhanced the performance up to 50%, and the enhancement becomes greater after accelerated durability tests. We verify via electrochemical impedance analyses, limiting current measurements, and multiphysics modeling that the enhancement is due to improved H+ and O2 transport. The work also demonstrates that the electrodes can be further improved by optimizing the electrode geometry, proven via machine learning investigations. These results inform next generation electrode designs for enhanced PEMFC performance and durability. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. Financial support for this work from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) is gratefully acknowledged (Projects 2020200DR and 20210915PRD2). ChungHyuk Lee acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

Advances and Challenges in Development of Transition Metal Catalysts for Heterogeneous Hydrogenation of Organic Compounds

AbstractActual problems of development of catalysts for hydrogenation of heterocyclic compounds by hydrogen are summarized and discussed. The scope of review covers composites of nanoparticles of platinum group metals and 3d metals for heterogeneous catalytic processes. Such problems include increase of catalyst activity, which is important for reduction of precious metals content; development of new catalytic systems which do not contain metals of platinum group or contain cheaper analogues of Pd; control of factors which make influence on the selectivity of the catalysts; achievement of high reproducibility of the catalyst‘s performance and quality control of the catalysts. Own results of the authors are also summarized and described. The catalysts were prepared by decomposition of Pd0 and Ni0 complexes, pyrolysis of Ni2+ and Co2+ complexes deposited on aerosil and reduction of Ni2+ in pores of porous support in situ. The developed catalysts were used for hydrogenation of multigram batches of heterocyclic compounds.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

Enabling the recycling of metals from the shredder light fraction derived from waste of electrical and electronic equipment via continuous pyrolysis process

The surge in Waste Electrical and Electronic Equipment (WEEE) generation, reaching 53.6 million metric tons (Mt) in 2019, demands efficient recycling solutions. This study focuses on the Shredder Light Fraction (SLF), a material stream derived from the mechanical pre-processing of WEEE, which is considered “municipal waste”. SLF constitutes 4.2% of the output material and is rich in metals like copper, tin, lead, zinc, silver, and gold.Pyrolysis treatment was applied to SLF, enabling recyclability. Both batch and continuous setups were employed for materials flow analysis and technical evaluation of the resource potential. The research evaluates the impact of pyrolysis technology on solid fraction metal content and pyrolysis gas/oil energy potential. Scaling up the process addressed material heterogeneity and increased the reliability of the obtained results.An innovative pyrometallurgical extraction approach was suggested, to recover valuable metals in SLF which otherwise could be lost via energy recovery methods. The resulting solid product after pyrolysis showed enriched concentrations of copper, zinc, lead, and precious metals with concentrations acceptable for industrial use. Additionally, it displayed reduced mass and diminished hazardous constituents.The non-condensable gas, rich in hydrogen, carbon monoxide, and methane, exhibited potential as an alternative energy source or reducing agent in the metallurgical sector.This research advances metal recycling from SLF, offering valuable insights for environmental impact mitigation as waste was transformed into a valuable by-product for potential use in the copper industry.

Metal-based electrocatalysts with data-driven designed particle size for hydrogen evolution

Metal-based catalysts are currently at the forefront of hydrogen evolution catalysts, yet the influence of particle size on their catalytic activity is intricate. In this study, we compiled a database using actual test results and employed interpretable algorithms to analyze the relationship of catalyst factors with their catalytic properties. Our analysis revealed a bowl-shaped correlation between the measured overpotential and the particle size of metal-based catalysts, with the optimal size falling within the range of 1.5 to 3.0 nm. To corroborate the algorithmic analysis, we synthesized nanoalloys using an ultrathin carbon layer, which effectively restricted the movement of metal atoms at high temperatures. The series of materials prepared displayed a consistent pattern in their measured overpotential, aligning with our algorithm’s prediction. Notably, the 2.0 nm PtCoNi catalyst achieved superior catalytic performance with lower precious metal content than commercial Pt/C. Further data-driven analysis indicates that the size-dependent catalytic activity is shaped by the balance between metal-support interaction and the exposure ratio of the active site. This study underscores the efficacy of merging a data-driven approach with precise control of material synthesis to analyze complex catalytic systems, providing a potent tool for future exploration in the field.

Noncovalent composites of meso-substituted A2B2-porphyrins and carbon nanotubes for enhanced electrocatalytic oxygen reduction

Exploring highly active oxygen reduction electrocatalysts with low precious metals content is imperative but remains a considerable challenge. Herein, a series of heterobimetallic multi-walled carbon nanotubes (MWCNTs) electrocatalysts based on metal complexes are presented. These electrocatalysts feature diverse transition metals (M=Mn, Fe, Co, Ni) 5,15-bromophenyl-10, 20-methoxyphenyl porphyrin (MBMP) and tetrakis(triphenylphosphine)palladium (0) (Pd[P(Ph3)4]) anchored non-covalently on its surface. The resulting NiBMP-based MWCNTs with Pd[P(Ph3)4] (PdNiN4/MWCNTs) display outstanding electrocatalytic oxygen reduction activity (onset potential, 0.941 V; half wave potential, 0.830 V) and robust long-term durability in alkaline electrolyte. While in neutral condition, the MnBMP-based MWCNTs with Pd[P(Ph3)4] (PdMnN4/MWCNTs) are the most active heterobimetallic ORR catalyst and produce ultra-low concentration hydrogen peroxide (H2O2 yield, 1.2%–1.3%). Synergistically tuning the ORR electrocatalytic activity and electron transfer pathway is achieved by the formation of NiBMP/MnBMP-Pd[P(Ph3)4] active sites. This work indicates such metalloporphyrin-Pd[P(Ph3)4] active sites on MWCNTs have significantly positive influence on electrocatalytic ORR systems and provides facile and mild strategy for designing highly efficient ORR electrocatalysts with ultra-low loading precious metal.