Nanoporous PtFe Nanoparticles Supported on N-Doped Porous Carbon Sheets Derived from Metal-Organic Frameworks as Highly Efficient and Durable Oxygen Reduction Reaction Catalysts

Pt Nanoparticles Confined in a 3D Porous FeNC Matrix as Efficient Catalysts for Rechargeable Li-CO2/O2 Batteries

The cathodic product Li₂CO₃, due to its high decomposition potential, has hindered the practical application of rechargeable Li-CO₂/O₂ batteries. To overcome this bottleneck, a Pt/FeNC cathodic catalyst is fabricated by dispersing Pt nanoparticles (NPs) with a uniform size of 2.4 nm and 8.3 wt % loading amount into a porous microcube FeNC support for high-performance rechargeable Li-CO₂/O₂ batteries. The FeNC matrix is composed of numerous two-dimensional (2D) carbon nanosheets, which is derived from an Fe-doping zinc metal-organic framework (Zn-MOF). Importantly, using Pt/FeNC as the cathodic catalyst, the Li-CO₂/O₂ (V_CO2/V_O2 = 4:1) battery displays the lowest overpotential of 0.54 V and a long-term stability of 142 cycles, which is superior to batteries with FeNC (1.67 V, 47 cycles) and NC (1.87 V, 23 cycles) catalysts. The FeNC matrix and Pt NPs can exert a synergetic effect to decrease the decomposition potential of Li₂CO₃ and thus enhance the battery performance. In situ Fourier transform infrared (FTIR) spectroscopy further confirms that Li₂CO₃ can be completely decomposed under a low potential of 3.3 V using the Pt/FeNC catalyst. Impressively, Li₂CO₃ exhibits a film structure on the surface of the Pt/FeNC catalysts by scanning electron microscopy (SEM), and its size can be limited by the confined space between the carbon sheets in Pt/FeNC, which enlarges the better contacting interface. In addition, density functional theory (DFT) calculations reveal that the Pt and FeNC catalysts show a higher adsorption energy for Li₂CO₃ and Li₂CO₄ intermediates compared to the NC catalyst, and the possible discharge pathways are deeply investigated. The synergetic effect between the FeNC support and Pt active sites makes the Li-CO₂/O₂ battery achieve optimal performance.

A novel three-dimensional flow-through graphite felt-matrix cathode for in-situ hydrogen peroxide generation in multi-environment systems-Multiphysics modeling for in-situ hydrogen peroxide generation

In order to achieve in-situ H₂O₂ generation in multi-environment systems, polyvinylpyrrolidone (PVP) and modified carbon nitride (t-g-C₃N₄) are co-doped onto graphite felt-matrix (GF-matrix) by electrodeposition to develop a novel cathode electrode. By means of 3D-X-ray CT, High-Resolution Transmission Electron Microscope (HRTEM), X-ray Photoelectron Spectrometer (XPS), Raman and Electrochemical Workstation, microscopic physical-chemical properties of materials are researched to optimize the electrode structure. Results show that the optimal electrode presents over H₂O₂ production rate of 2000 mgL^-1·h^-1, and as high as current efficiency of 93% to 98% in simulated freshwater (50 mM Na₂SO₄, pH = 1-12) at 20 mAcm^-2. Furthermore, we built an original three-dimensional (3D) flow-through GF-matrix cathode model on H₂O₂ generation in simulated freshwater, explaining solution pH change reasons from solution inlet to outlet.

Mo-Doped FeP Nanospheres for Artificial Nitrogen Fixation

Electrochemical conversion of N₂ to NH₃ under ambient conditions is a promising and environmentally friendly route compared with the CO₂-emitting and energy-intensive Haber-Bosch process. Nevertheless, due to ultrahigh stability of N₂, it is urgent to explore efficient catalysts to weaken and activate the N≡N bond. Here, we report the Mo-doped iron phosphide (Mo-FeP) nanosphere as a valid transition-metal-based catalyst for electrochemical N₂-to-NH₃ fixation under ambient conditions. This catalyst exhibits excellent catalytic performance with a NH₄⁺ yield rate (13.1 μg h^-1 mg^-1) and Faradaic efficiency (7.49%) at -0.3 and -0.2 V vs reversible hydrogen electrode (RHE), respectively. However, the FeP catalyst without doped Mo species displays weak catalytic performance. We found that the better catalytic performance of Mo-FeP might be due to the doping of Mo species, which is favorable for the polarization of adsorbed N₂ molecules, making the N≡N bond more viable to dissociate.

A Dewetted-Dealloyed Nanoporous Pt Co-Catalyst Formed on TiO2 Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H2 Production

Pt nanoparticles are typically decorated as co-catalyst on semiconductors to enhance the photocatalytic performance. Due to the low abundance and high cost of Pt, reaching a high activity with minimized co-catalyst loadings is a key challenge in the field. We explore a dewetting-dealloying strategy to fabricate on TiO2 nanotubes nanoporous Pt nanoparticles, aiming at improving the co-catalyst mass activity for H2 generation. For this, we sputter first Pt-Ni bi-layers of controllable thickness (nm range) on highly ordered TiO2 nanotube arrays, and then induce dewetting-alloying of the Pt-Ni bi-layers by a suitable annealing step in a reducing atmosphere: the thermal treatment causes the Pt and Ni films to agglomerate and at the same time mix with each other, forming on the TiO2 nanotube surface metal islands of a mixed PtNi composition. In a subsequent step we perform chemical dealloying of Ni that is selectively etched out from the bimetallic dewetted islands, leaving behind nanoporous Pt decorations. Under optimized conditions, the nanoporous Pt-decorated TiO2 structures show a>6 times higher photocatalytic H2 generation activity compared to structures modified with a comparable loading of dewetted, non-porous Pt. We ascribe this beneficial effect to the nanoporous nature of the dealloyed Pt co-catalyst, which provides an increased surface-to-volume ratio and thus a more efficient electron transfer and a higher density of active sites at the co-catalyst surface for H2 evolution.

Hollow PtFe Alloy Nanoparticles Derived from Pt-Fe3 O4 Dimers through a Silica-Protection Reduction Strategy as Efficient Oxygen Reduction Electrocatalysts

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO₂ -coated Pt-Fe₃ O₄ nanoparticle dimers supported on carbon at 900 °C, followed by SiO₂ shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO₂ protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO₂ coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.

N,P Co-Coordinated Manganese Atoms in Mesoporous Carbon for Electrochemical Oxygen Reduction

The increasing interest in fuel cell technology encourages the development of efficient and low-cost electrocatalysts to replace the Pt based materials for catalyzing the cathodic oxygen reduction reaction (ORR). In the present work, a nitrogen and phosphorus co-coordinated manganese atom embedded mesoporous carbon composite (MnNPC-900) is successfully prepared via a polymerization of o-phenylenediamine followed by calcination at 900 °C. The MnNPC-900 composite shows a high ORR activity in alkaline media, offering an onset potential of 0.97 V, and a half-wave potential of 0.84 V (both vs reversible hydrogen electrode) with a loading of 0.4 mg cm^-2 . This performance not only exceeds its phosphorus-free counterpart (MnNC-900), but also is comparable to the Pt/C catalyst under identical measuring conditions. The significantly enhanced ORR performance of MnNPC-900 can be ascribed to: i) the introduction of phosphorus assists the generation of mesopores during the pyrolysis and endows the MnNPC-900 composite with large surface area and pore volume, thus facilitating the mass transfer process and increases the number of exposed active sites. ii) The formation of N,P co-coordinated atomic-scale Mn sites (MnN_x P_y ), which modifies the electronic configuration of the Mn atoms and thereby boosts the ORR catalytic activity.

Enhancing the Capacitance of Battery-Type Hybrid Capacitors by Encapsulating MgO Nanoparticles in Porous Carbon as Reservoirs for OH- Ions from Electrolytes

A novel design of no-loading and bifunctional positive electrode, serving as an active material and current collector simultaneously, has been constructed by grass-like nickel foam which shows a battery-type performance and excellent areal specific capacity at 0.540 mA h·cm^-2 (over 4500 mF·cm^-2). To obtain a high-performance hybrid capacitor, layered porous carbonaceous composites C/MgO negative electrodes were fabricated, in which MgO nanoparticles serve as "reservoirs" for OH^- ions from the electrolyte. Compared with other carbon materials, such as carbon fibers, hollow nanospheres, and nanotubes, the three-dimensional (3D) hierarchical heterostructures of the C/MgO electrode exhibit a higher storage performance of 424.1 mF·cm^-2. Assembled by these two working electrodes, a hybrid capacitor with uncommon galvanostatic charge/discharge cycling curve has been well-investigated in an alkaline aqueous electrolyte system. This as-coupled hybrid capacitor exhibits an engaging activation process during multiple cycling tests and leads to a drastically improved energy density of 60% (from 80.4 to 128.8 μW h·cm^-2), which can be attributed to a "match behavior" between its positive and negative electrodes.

Corrosion Engineering To Synthesize Ultrasmall and Monodisperse Alloy Nanoparticles Stabilized in Ultrathin Cobalt (Oxy)hydroxide for Enhanced Electrocatalysis

Two-dimensional (2D) nanomaterials decorated with ultrasmall and well-alloyed bimetallic nanoparticles (NPs) have many important applications. Developing a facile and scalable 2D material/hybrid synthesis strategy is still a big challenge. Herein, a top-down corrosion strategy is developed to prepare ultrathin cobalt (oxy)hydroxide nanosheets decorated with ultrasmall (∼1.6 nm) alloy NPs. The formation of ultrathin (oxy)hydroxide nanosheets has a restrain effect to prevent the growth of small NPs into bigger ones. Thanks to the ultrathin 2D nature and strong electronic interaction between Co(OH)₂ and alloy NPs, the Pt-based binary alloy NPs are greatly stabilized by the Co(OH)₂ nanosheets and the hybrids exhibit much enhanced electrocatalytic performance for water splitting. Especially, the mass activities of the PtPd- and PtCu-decorated samples for hydrogen evolution are ∼8 times that of Pt/C. When used as both cathode and anode electrocatalysts to split water, the hybrid nanosheets outperform the commercial Pt/C-RuO₂ combination. At 10 mA cm^-2, the needed potential is only 1.53 V. This work provides us a highly controllable and scalable means to produce clean 2D nanomaterials decorated with a series of alloy NPs such as PtPd, PtCu, AuNi, and so forth.

Applications of Metal-Organic-Framework-Derived Carbon Materials

Carbon materials derived from metal-organic frameworks (MOFs) have attracted much attention in the field of scientific research in recent years because of their advantages of excellent electron conductivity, high porosity, and diverse applications. Tremendous efforts are devoted to improving their chemical and physical properties, including optimizing the morphology and structure of the carbon materials, compositing them with other materials, and so on. Here, many kinds of carbon materials derived from metal-organic frameworks are introduced with a particular focus on their promising applications in batteries (lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries), supercapacitors (metal oxide/carbon and metal sulfide/carbon), electrocatalytic reactions (oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction), water treatment (MOF-derived carbon and other techniques), and other possible fields. To close, some existing problem and corresponding possible solutions are proposed based on academic knowledge from the reported literature, along with a great deal of experimental experience.

Low Pt Alloyed Nanostructures for Fuel Cells Catalysts

Low-noble metal electrocatalysts are attracting massive attention for anode and cathode reactions in fuel cells. Pt transition metal alloy nanostructures have demonstrated their advantages in high performance low-noble metal electrocatalysts due to synergy effects. The basic of designing this type of catalysts lies in understanding structure-performance correlation at the atom and electron level. Herein, design threads of highly active and durable Pt transition metal alloy nanocatalysts are summarized, with highlighting their synthetic realization. Microscopic and electron structure characterization methods and their prospects will be introduced. Recent progress will be discussed in high active and durable Pt transition metal alloy nanocatalysts towards oxygen reduction and methanol oxidation, with their structure-performance correlations illustrated. Lastly, an outlook will be given on promises and challenges in future developing of Pt transition metal alloy nanostructures towards fuel cells catalysis uses.

Ultrasmall Ru/Cu-doped RuO2 Complex Embedded in Amorphous Carbon Skeleton as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Developing highly active electrocatalysts with superior durability for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the same electrolyte is a grand challenge to realize the practical application of electrolysis water for producing hydrogen. In this work, an ultrasmall Ru/Cu-doped RuO₂ complex embedded in an amorphous carbon skeleton is synthesized, through thermolysis of Ru-modified Cu-1,3,5-benzenetricarboxylic acid (BTC), as a highly efficient bifunctional catalyst for overall water splitting electrocatalysis. The ultrasmall Ru nanoparticles in the complex expose more activity sites for hydrogen evolution and outperform the commercial Pt/C. Meanwhile, the ultrasmall RuO₂ nanoparticles exhibit superior oxygen evolution performance over commercial RuO₂, and the doping of Cu into the ultrasmall RuO₂ nanoparticles further enhances the oxygen evolution performance of the catalyst. The outstanding OER and decent HER catalytic activity endow the complex with impressive overall water splitting performance superior to that of the state-of-the-art electrocatalysts, which just require 1.47 and 1.67 V to achieve a current density of 10 mA cm^-2 and 100 mA cm^-2. The density functional theory calculations reveal that a Cu dopant could effectively tailor the d-band center, thereby tuning electronic structure of Ru activity sites on the RuO₂ (110) plane and ultimately improving the OER performance of RuO₂.

Gallic acid-assisted synthesis of Pd uniformly anchored on porous N-rGO as efficient electrocatalyst for microbial fuel cells

The sluggish kinetic rate-limiting oxygen reduction reaction (ORR) at the cathode remains the foremost issue hindering the commercialization of microbial fuel cells (MFCs). Utilization of the effect of micromolecule conjugation and the synergistic effect between Pd nanoparticles and N-rGO (nitrogen-doped reduced graphene oxide) to stabilize a precious metal onto carbon materials is a promising strategy to design and synthesize highly efficient cathode catalysts. In this study, gallic acid is used to facilitate the coupling of palladium (Pd) with N-rGO to form GN@Pd-GA via a simple hydrothermal process. Notably, the as-synthesized GN@Pd-GA as a cathode catalyst shows an approximately direct four-electron feature and demonstrates a high ORR performance in 0.1 M KOH. Furthermore, the stability and methanol tolerance of GN@Pd-GA are superior to those of the commercial Pt/C catalysts. In addition, a maximum power density of 391.06 ± 0.2 mW m^-2 of MFCs equipped with GN@Pd-GA was obtained, which was 96.2% of the power density of MFCs equipped with a commercial Pt/C catalyst.

Tungsten nitride/carbide nanocomposite encapsulated in nitrogen-doped carbon shell as an effective and durable catalyst for hydrogen evolution reaction

In situ carbonized WO_X/aniline hybrid nanoparticles were prepared and used to obtain WN–W₂C nanocomposites encapsulated in nitrogen-doped carbon shell, which demonstrated excellent HER performance.