Black Catalyst Research Articles

I3‐‐Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc‐Air Battery Performance with Low Charging Voltage and Long Cycling Life

An effective strategy to facilitate oxygen redox chemistry in metal‐air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn‐air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3‐‐mediated Zn‐air battery by using ZnI2 additives that provide I3‐ to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn‐air battery performs an ultra‐long cycle life of over 600 h at 5 mA cm‐2 with a final charge voltage of 1.87 V. We demonstrate that I‐ mainly generates I3‐ on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH‐ to generate oxygen and further revert to I‐, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn‐air batteries through redox mediator methods.

I3--Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc-Air Battery Performance with Low Charging Voltage and Long Cycling Life.

An effective strategy to facilitate oxygen redox chemistry in metal-air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn-air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3--mediated Zn-air battery by using ZnI2 additives that provide I3- to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn-air battery performs an ultra-long cycle life of over 600 h at 5 mA cm-2 with a final charge voltage of 1.87 V. We demonstrate that I- mainly generates I3- on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH- to generate oxygen and further revert to I-, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn-air batteries through redox mediator methods.

Enriched Oxygen Coverage Localized within Ir Atomic Grids for Enhanced Oxygen Evolution Electrocatalysis.

Inefficient active site utilization of oxygen evolution reaction (OER) catalysts have limited the energy efficiency of proton exchange membrane (PEM) water electrolysis. Here, an atomic grid structure is demonstrated composed of high-density Ir sites (≈10atoms per nm2) on reactive MnO2-x support which mediates oxygen coverage-enhanced OER process. Experimental characterizations verify the low-valent Mn species with decreased oxygen coordination in MnO2-x exert a pivotal impact in the enriched oxygen coverage on the surface during OER process, and the distributed Ir atomic grids, where highly electrophilic Ir─O(II-δ)- bonds proceed rapidly, render intense nucleophilic attack of oxygen radicals. Thereby, this metal-support cooperation achieves ultra-low overpotentials of 166mV at 10mA cm-2 and 283mV at 500mA cm-2, together with a striking mass activity which is 380 times higher than commercial IrO2 at 1.53V. Moreover, its high OER performance also markedly surpasses the commercial Ir black catalyst in PEM electrolyzers with long-term stability.

Microstructural Design of PEFC Electrocatalyst Layer Using Mesoporous Carbon

Heavy-duty applications of polymer electrolyte fuel cells (PEFCs) require improved activity and durability of the cathode electrocatalysts. The nanostructure and microstructure of the catalyst layer both significantly affect PEFC performance. Mesoporous carbons (MC) have mesopores which have been shown to suppress ionomer poisoning, when used as a catalyst support, leading to higher catalytic activity. Here, we compare the initial performance of single cells using Ketjen black (KB) and MC catalyst supports. Furthermore, the fuel cell performance is evaluated using Pt-Ta-Co alloy-based catalyst decorated on MC. Pt-Ta-Co/MC electrocatalyst exhibits high cell performance in a low current density range. However, cell performance at high current densities has yet to be improved due to non-uniform microstructure of the Pt-Ta-Co/MC electrocatalyst layer.

Microstructural Design of PEFC Electrocatalyst Layer Using Mesoporous Carbon

Heavy-duty applications of polymer electrolyte fuel cells (PEFCs) require improved activity and durability of the cathode electrocatalysts. The nanostructure and microstructure of the catalyst layer both significantly affect PEFC performance. Mesoporous carbons (MC) have mesopores which have been shown to suppress ionomer poisoning, when used as a catalyst support, leading to higher catalytic activity. Here, we compare the initial performance of single cells using Ketjen black (KB) and MC catalyst supports. Furthermore, the fuel cell performance is evaluated using Pt-Ta-Co alloy-based catalyst decorated on MC. Pt-Ta-Co/MC electrocatalyst exhibits high cell performance in a low current density range. However, cell performance at high current densities has yet to be improved due to non-uniform microstructure of the Pt-Ta-Co/MC electrocatalyst layer.

Activity and Stability of Iridium-Based Alloy Catalysts for PEM Electrolyzer

Bi-metallic alloy of Ir3Cr and Ir3Pt catalysts as well as Ir black as reference were synthesized by co-reduction route in sodium borohydride under hydrothermal condition. Well-distributed particles in the range of 1.7 - 2 nm in average were yielded. Ir alloy formation was confirmed by XRD spectra. Interestingly, after 1000 ADT cycle under half cell condition, Ir3Cr catalyst showed an enhanced activity of 7% and 59% for OER at 1.6 V compared to Ir3Pt and as prepared Ir black, respectively. Moreover, both alloy catalysts exhibited excellent stability with ~10 and 40 mV less overpotential for OER at 20 mA cm-2 compared to as-synthesized Ir black and commercial Ir black catalysts.

Engineering p-d orbital hybridization in PdSb bimetallene for energy-saving H2 production parallel upgrade plastic waste

The electrochemical conversion of PET-derived ethylene glycol into high-quality chemicals parallel energy-saving H2 production is an optimal solution to the serious environmental pollution of plastics. In this paper, p-d orbital hybrid PdSb bimetallene with defect-rich crimped surface is synthesized by a one-step solvent approach. PdSb bimetallene exhibits excellent electrocatalytic performance in ethylene glycol and PET hydrolysate oxidation attributed to the unconventional p-d orbital hybridization feature and metallene structure. PdSb bimetallene shows better properties than Pd metallene and commercial Pd black catalysts under ethylene glycol conditions and PET hydrolysate. Besides PdSb bimetallene can oxidize ethylene glycol to produce the valuable product glycolic acid with high Faradaic efficiency and selectivity. Besides, PdSb bimetallene can oxidize PET-derived ethylene glycol into glycolic acid with high selectivity in EGOR||HER system. This study provides insights into the synthesis of metallene with p-d orbital hybridization properties, coupled with energy-saving H2 production parallel upgrade plastic waste.

Constructing alkaline microenvironment on catalyst surface for enhanced electrocatalytic synthesis of hydrogen peroxide in a neutral electrolyte

The direct electrochemical synthesis of H2O2 via a two-electron oxygen reduction reaction (2e− ORR) offers a feasible alternative to the energy-intensive anthraquinone oxidation process. Compared to alkaline electrolytes, challenges remain in achieving high 2e− ORR selectivity and activity for electrosynthesis of H2O2 in neutral electrolytes due to the low concentration of OH−, which hinders the effective binding of key intermediate OOH*. Here, we introduced Lewis acid TiO2 to modify carbon black catalyst for adsorbing in-situ generated OH− and created a local alkaline microenvironment for enhancing the 2e− ORR activity and selectivity in neutral electrolytes. H2O2 productivity of TiO2 modified carbon black catalyst (52.5 mmol L−1 h−1) in a neutral electrolyte (0.5 M Na2SO4) at 0.2 V vs. RHE was 1.6 times as much as that of pristine carbon black (33 mmol L−1 h−1), which was similar with that of pristine carbon black (58.4 mmol L−1 h−1) in an alkaline electrolyte (0.1 M KOH). The finite-element method simulations and experiments indicated that TiO2 could enhance local alkalinity to increase the current density for facilitating 2e− ORR. The density functional theory calculations indicated that the introducing of TiO2 into the CB structure could promote the adsorption of O2, facilitate the adsorption of *OOH and reduce the overpotential, resulting in high activity towards 2e− ORR to H2O2. This work proposes a new strategy for optimizing electrode–electrolyte interface to enhance 2e− ORR performance in neutral electrolytes.

Anionic Surfactant-Modulated Electrode-Electrolyte Interface Promotes H2O2 Electrosynthesis.

Conventional strategies for highly selective and active hydrogen peroxide (H2O2) electrosynthesis primarily focus on catalyst design. Electrocatalytic reactions take place at the electrified electrode-electrolyte interface. Well-designed electrolytes, when combined with commercial catalysts, can be directly applied to high-efficiency H2O2 electrosynthesis. However, the role of electrolyte components is equally crucial but is significantly under-researched. In this study, anionic surfactant n-tetradecylphosphonic acid (TDPA) and its analogs are used as electrolyte additives to enhance the selectivity of the two-electron oxygen reduction reaction. Mechanistic studies reveal that TDPA assembled over the electrode-electrolyte interface modulates the electrical double-layer structure, which repels interfacial water and weakens the hydrogen-bond network for proton transfer. Additionally, the hydrophilic phosphonate moiety affects the coordination of water molecules in the solvation shell, thereby directly influencing the proton-coupled kinetics at the interface. The TDPA-containing catalytic system achieves a Faradaic efficiency of H2O2 production close to 100% at a current density of 200mA cm-2 using commercial carbon black catalysts. This research provides a simple strategy to enhance H2O2 electrosynthesis by adjusting the interfacial microenvironment through electrolyte design.

Ultrafast solid-state microwave fabrication of CoFe2O4@carbon black composite with coupling reinforcement effect towards actualizing effective water decontamination

Due to the synergistic redox coupling between the two metals, cobalt ferrite-based materials demonstrate stable degradation properties for organic pollutants by activating peroxomonosulfate (PMS). However, the challenge lies in developing the simplest and fastest methods to construct and modulate cobalt ferrite composites. In this study, CoFe2O4 nanoparticle-integrated carbon black composite catalysts (CoFe2O4-CB-x) were prepared using an environmentally friendly solid-state microwave method. The CoFe2O4-CB-120 catalyst showed excellent efficiency in degrading tetracycline (TC) through PMS activation, achieving a removal rate of nearly 90 % in 30 min with an apparent rate constant of 0.1232 min−1. The catalyst also effectively degraded various organic compounds and real-life wastewater by almost 80 %, promising application potential. Furthermore, CoFe2O4-CB-120 maintained its high activity after five cycles, attributed to its its magnetic properties facilitating good separation and preventing catalyst loss during cycling tests. The degradation mechanism of the CoFe2O4-CB-120/PMS system was thoroughly investigated, identifying key active species such as SO4•−, •OH, and 1O2, with proposed pathways for TC degradation. This study presents an innovative, simple, and efficient strategy for producing spinel cobalt ferrite and carbon composites for PMS activation in organic pollutant degradation.

Highly selective chemical reduction of nitrate in water in carbon-based contactor catalytic membrane reactors

A carbon-based catalytic membrane reactor in a contactor (interfacial) configuration has been used as an approach to control selectivity in the reduction of NO3- in water. Water and hydrogen fed to the reactor circulate tangentially on opposite sides of the membrane, which acts as a separator and contactor, enabling hydrogen transfer to the water phase. Powdered carbons (carbon black, carbon nanofiber, and activated carbon) were used to prepare catalytic membranes that also acted as contactors to transfer H2 from the gas phase to water. The membranes based on the Pd-Cu/carbon black catalyst showed lower selectivity towards unwanted NH4+ than the Pd-Cu and Pd-Sn catalysts supported on carbon nanofibers and activated carbon, due to a good balance among conductivity, external surface area, and particle size. Sensitivity analysis for H2 partial pressure demonstrated that the contactor membrane reactor can be operated with control of H2 mass transfer, hence enabling enhanced control of the selectivity to NH4+. Additional control of selectivity was achieved by reducing the catalytic layer thickness of the membrane, which improved NO3- transport and decreased the H/N ratio at the active centers. With these approaches, NO3- conversion values above 40 % with negligible NH4+ production and NO3- conversions close to 60 % with NH4+ selectivity values around 3 % were achieved.

Theoretical study of the mechanism of hydrogen production by catalytic methane decomposition on the carbon black catalyst

Catalytic methane decomposition (CMD) is a promising chemical process for hydrogen production from natural gas with zero CO2 emissions. In the present work we perform a systematic study of CMD on the graphene edge as a model of the carbon catalyst surface. Atomistic first-principles calculations (DFT level of theory) were performed to obtain the parameters of elementary reactions including the formation of active sites, interaction of methane molecules with these active sites and regeneration of the carbon catalyst surface. Our findings show that methane pyrolysis on the carbon catalyst is a unique heterogeneous radical chain process in which active sites are migrating over the catalyst surface via gas phase radical transport. Based on quantum-chemistry calculations, detailed kinetic mechanism of CMD on the carbon catalyst was developed and verified with respect to the latest experimental data. Calculated effective activation energies and methane conversions in CMD process are in reasonable agreement with experimental data. The present investigation of the mechanism of hydrogen production by CMD process on carbon catalyst can be useful for optimization of this process taking into account degradation of the carbon catalyst.

Electrocatalytic Decomposition of Lithium Oxalate-Based Composite Microspheres as a Prelithiation Additive in Lithium-Ion Batteries.

In conventional lithium-ion batteries (LIBs), the active lithium from the lithium-containing cathode is consumed by the formation of a solid electrolyte interface (SEI) at the anode during the first charge, resulting in irreversible capacity loss. Prelithiation additives can provide additional active lithium to effectively compensate for lithium loss. Lithium oxalate is regarded as a promising ideal cathode prelithiation agent; however, the electrochemical decomposition of lithium oxalate is challenging. In this work, a hollow and porous composite microsphere was prepared using a mixture of lithium oxalate, Ketjen Black and transition metal oxide catalyst, and the formulation was optimized. Owing to the compositional and structural merits, the decomposition voltage of lithium oxalate in the microsphere was reduced to 3.93 V; when being used as an additive, there is no noticeable side effect on the performance of the cathode material. With 4.2% of such an additive, the first discharge capacity of the LiFePO4‖graphite full cell increases from 139.1 to 151.9 mAh g-1, and the coulombic efficiency increases from 88.1% to 96.3%; it also facilitates the formation of a superior SEI, leading to enhanced cycling stability. This work provides an optimized formula for developing an efficient prelithiation agent for LIBs.

Retraction: "Water splitting system with a 13.1% solar to hydrogen conversion efficiency using 3-junction III-V solar cells with pulse plated Pt black catalyst"

Retraction The authors hereby retract the above article. This paper reports on a highly efficient system for water splitting using a three-junction solar cell with a platinum black catalyst under simulated sunlight. After this manuscript was accepted, it was found that there was an error in the conditions for electroplating the platinum black catalyst on the solar cell. Specifically, there was an error in the settings for the pulse power supply used when plating platinum black. Although the pulse current, pulse width, and cycle were set correctly, the base current value was the same as the pulse current, which was found in a separate experiment using the same equipment. The authors checked the current output under the conditions described in this manuscript using an oscilloscope, and it was confirmed that it was a direct current, not a pulsed current. The measurement results for hydrogen production under simulated sunlight irradiation presented in the paper were correct, and the conclusions regarding hydrogen production were also correct. However, there was an error in the plating conditions for platinum black described in the paper, and the title and content of the discussion also needed to be revised. Based on the above, the authors reached the consensus that the above paper should be retracted and that the authors will submit it again as a new paper with no mistakes in the Japanese Journal of Applied Physics.

Recovered carbon black from tires as carbon carrier in metal oxide catalytic systems

Pyrolysis is one of the most common methods of end-of-life tires (ELTs) recycling. This study considered the use of carbon black from pyrolysis of ELTs as a carbon carrier for metals (Co, Ni, Cu, Fe) and their oxides to produce catalytic systems. The synchronous thermal analysis showed the positive effect of metal oxides/recovered carbon black (MOs/rCB) on ammonium perchlorate thermolysis. It was selected as a model catalytic reaction. Metal oxides/recovered carbon black (MOs/rCB) catalysts facilitated a reduction in the thermal decomposition phases of ammonium perchlorate, resulting in a significant narrowing of the decomposition interval. The greatest narrowing (22.7 °C) was observed at 103.5 °C for non-catalytic process. All tri-metallic catalytic systems showed high catalytic efficiency, providing a narrowing of the decomposition interval on average 2.5 times more in comparison with mono-metallic catalysts. Trioxide catalyst CuO/CoO/FeO/rCB showed the most significant shift in the high-temperature decomposition stage by 13% (from 334.0 °C to 293.2 °C). The activity of di-, tri-, and tetra-metallic catalytic systems was further enhanced by the synergistic effect induced by the addition of a second (or more) metal to the system. Efficient use of rCB for impregnated catalyst systems production could improve the economic efficiency of ELTs pyrolysis.

Heterointerface engineering of rhombic Rh nanosheets confined on MXene for efficient methanol oxidation

Although metallic rhodium (Rh) is regarded as a promising platinum-alternative anode catalyst of direct methanol fuel cell (DMFC), the conventional “particle-to-face” contact model between Rh and matrix largely limits the overall electrocatalytic performance due to their insufficient cooperative effects. Herein, we report a controllable and robust heterointerface engineering strategy for the bottom-up fabrication of rhombic Rh nanosheets in situ confined on Ti3C2Tx MXene nanolamellas (Rh NS/MXene) via a convenient stereoassembly process. This unique design concept gives the resulting 2D/2D Rh NS/MXene heterostructure intriguing textural features, including large accessible surface areas, strong “face-to-face” interfacial interactions, homogeneous Rh nanosheet distribution, ameliorative electronic structure, and high electronic conductivity. As a consequence, the as-prepared Rh NS/MXene nanoarchitectures exhibit exceptional electrocatalytic methanol oxidation properties in terms of a large electrochemically active surface area of 126.2 m2 g−1Rh, a high mass activity of 1056.9 mA mg−1Rh, and a long service life, which significantly outperform those of conventional particle-shaped Rh catalysts supported by carbon black, carbon nanotubes, reduced graphene oxide, and MXene matrixes as well as the commercial Pt nanoparticle/carbon black and Pd nanoparticle/carbon black catalysts with the same noble metal loading amount. Density functional theory calculations further demonstrate that the direct electronic interaction at the well-contacted 2D/2D heterointerfaces effectively enhances the adsorption energy of Rh nanosheets and induces a left shift of the d-band center, thereby making the Rh NS/MXene configuration suffer less from CO poisoning. This work highlights the importance of rational heterointerface design in the construction of advanced noble metal/MXene electrocatalysts, which may provide new avenues for developing the next-generation DMFC devices.

Iridium nanoparticles supported on polyaniline nanotubes for peroxidase mimicking towards total antioxidant capacity assay of fruits and vegetables

In this study, a straightforward approach is presented for the first time to anchor Ir nanoparticles on the surface of uniform polyaniline (PANi) nanotubes (NTs), which can be used as an efficient peroxidase (POD)-like catalyst. The morphology and chemical structure of the PANi-Ir nanocomposite are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. Owing to the strong interaction between Ir nanoparticles and PANi, a remarkable catalytic enhancement is achieved compared to the bare Ir black catalyst and individual PANi NTs, dominating withan electron transfer mechanism. Furthermore, an efficient colorimetric sensor for ascorbic acid (AA) is developed with a low detection limit of 1.0 μM (S/N = 3), and a total antioxidant capacity (TAC) sensing platform is also constructed for the rigorous detection and analysis of fruits and vegetables.

Hydrogen Peroxide Electrosynthesis in a Strong Acidic Environment Using Cationic Surfactants.

The two-electron oxygen reduction reaction (2e--ORR) can be exploited for green production of hydrogen peroxide (H2O2), but it still suffers from low selectivity in an acidic electrolyte when using non-noble metal catalysts. Here, inspired by biology, we demonstrate a strategy that exploits the micellization of surfactant molecules to promote the H2O2 selectivity of a low-cost carbon black catalyst in strong acid electrolytes. The surfactants near the electrode surface increase the oxygen solubility and transportation, and they provide a shielding effect that displaces protons from the electric double layer (EDL). Compared with the case of a pure acidic electrolyte, we find that, when a small number of surfactant molecules were added to the acid, the H2O2 Faradaic efficiency (FE) was improved from 12% to 95% H2O2 under 200 mA cm-2, suggesting an 8-fold improvement. Our in situ surface enhanced Raman spectroscopy (SERS) and optical microscopy (OM) studies suggest that, while the added surfactant reduces the electrode's hydrophobicity, its micelle formation could promote the O2 gas transport and its hydrophobic tail could displace local protons under applied negative potentials during catalysis, which are responsible for the improved H2O2 selectivity in strong acids.

Carbon nanotube-bridged MXene nanoarchitectures decorated with ultrasmall Rh nanoparticles for efficient methanol oxidation

Rational design and precise synthesis of cost-effective and highly-active Pt-alternative anode catalysts are important paths to accelerate the application and promotion of direct methanol fuel cell. Herein, a robust and controllable synthetic strategy is developed to bottom-up construction of carbon nanotube-bridged Ti3C2Tx MXene nanoarchitectures decorated with ultrasmall Rh nanoparticles (denoted as Rh/CNT-MX) through a facile co-assembly process. The existence of MXene nanosheets with abundant anchoring sites can immobilize nano-sized Rh crystals and facilitate their dispersion, while the integration of CNT skeletons effectively separates the neighboring MXene layers and offers unimpeded electron transport channels, which are conducive to making full use of respective catalytic functions for each component. As a consequence, the optimized Rh/CNT-MX catalyst expresses superior methanol oxidation performance with a considerable electrochemically active surface area of 89.4 m2/g, high mass/specific activity of 911.0 mA/mg/1.02 mA/cm2, and reliable long-term durability, which has obvious competitive advantages over the conventional Rh/carbon black, Rh/CNT, Rh/MXene, as well as commercial Pt/carbon black and Pd/carbon black catalysts.

Enhanced electrocatalytic performance of PtNi bimetallic alloys on carbon nanotube for ethanol oxidation reaction

In this paper, Ni-Pt bimetallic alloy nanoparticles were loaded on carbon nanotubes to prepare Ni-Pt nanoparticles/carbon nanotubes composites (Ni-Pt NPs/CNTs) as excellent catalytic materials for ethanol electro-oxidation reaction (EOR). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and special aberration corrected transmission electron microscope (STEM) were used to characterize its morphology and structure. The activity and stability of the composite were measured by cyclic voltammetry (CV) and chronoamperometry (CA). The catalytic performance was explored by adjusting the ratio of Ni to Pt. Performance test results showed that the Ni-Pt alloy formed 10–15 nm spherical particles and dispersed uniformly on the surface of carbon nanotubes. The Ni1Pt1 NPs/CNTs composite showed excellent performance for EOR. Its mass activity of ethanol electro-oxidation was 620 mA·mg−1Pt, which was 5.08, 18.2 times higher than that of commercial Pt/C and Pt black catalyst, respectively.