TePtFe Nanotubes as High-Performing Bifunctional Electrocatalysts for the Oxygen Reduction Reaction and Hydrogen Evolution Reaction

Integrating Pt16 Te Nanotroughs and Nanopillars into a 3D "Self-Supported" Hierarchical Nanostructure for Boosting Methanol Electrooxidation

To develop durable and low-price catalysts of methanol oxidation to commercialize direct methanol fuel cell, many attempts have been made at fabricating Pt-based hybrids by designing component-, morphology-, facet-, integration-pattern-varied nanostructures, and have achieved considerable successes. However, most of present catalysts still lack robust catalytic durability especially owing to the corrosion of mixed carbon and the poor mechanical stability of catalyst layer. Herein, Te nanowire array is transformed at an air/water interface into a 3D Pt₁₆ Te hierarchical nanostructure via an interface-confined galvanic replacement reaction. As-formed Pt₁₆ Te nanostructure has an asymmetrical architecture composed of nanotroughs and nanopillars, and nanopillars are perpendicular to nanotroughs with a loose arrangement. Pt₁₆ Te hierarchical nanostructure has a "self-supported" feature and, when directly used as the catalyst of methanol electrooxidation, exhibits superior catalytic activity (>four times larger in mass activity than state-of-the-art Pt/C in either acidic or basic solution) and long-term durability (after 500 cycles of cyclic voltammetric measurement, more than 55% of the initial specific activity remains whereas Pt/C only remains 22.2% in acidic solution and almost loses all activity in basic solution). This study fully demonstrates that designing "self-supported" catalyst film may be the next promising step for improving the catalytic performance of Pt-based hybrids.

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR

Efficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm-2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

One-dimensional nitrogen-doped carbon frameworks embedded with zinc-cobalt nanoparticles for efficient overall water splitting

Metal-organic frameworks (MOFs)-derived catalysts exhibit highly-efficient hydrogen or oxygen evolution performance on water splitting. However, it is an urgent problem to construct bifunctional electrocatalysts for both hydrogen and oxygen evolution performance. Herein, we adopted Ag nanowires as templates to prepare one-dimensional Ag nanowire@ZIF-8@ZIF-67 precursors (1D AgNW@ZIF-8@ZIF-67). Through pyrolysis, AgNW@ZIF-8@ZIF-67 precursors transformed into nitrogen-doped carbon frameworks (NCF) embedded with zinc-cobalt (ZnCo) nanoparticles on the surface of Ag NWs (denoted as Ag@ZnCo/NCF nanohybrids). The nanohybrids were consisted of Ag NWs with good conductivity and ZnCo/NCF nanohybrids with rich accessible active sites. Benefiting from their large specific surface area, accessible active sites and synergistic effect among components, Ag@ZnCo/NCF nanohybrids exhibit lower overpotentials of 139 mV and 279 mV at the current density of 10 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution, severally. Compared with other catalysts, Ag@ZnCo/NCF nanohybrids possess smaller Tafel slope, indicating their higher catalytic activity. This work provides a new perspective for designing low-cost and highly efficient bifunctional electrocatalysts for overall water splitting.

Basal-Plane Catalytic Activity of Layered Metallic Transition Metal Ditellurides for the Hydrogen Evolution Reaction

We report the electrochemical hydrogen evolution reaction (HER) of two-dimensional metallic transition metal dichalcogenides (TMDs). TMTe2 (TM: Mo, W, and V) single crystals were synthesized and characterized by optical microscopy, X-ray diffraction, and electrochemical measurements. We found that TMTe2 acts as a HER-active catalyst due to the inherent catalytic activity of its basal planes. Among the three metallic TMTe2, VTe2 shows the best HER performance with an overpotential of 441 mV and a Tafel slope of 70 mV/dec. It is 668 mV and 137 mV/dec for MoTe2 and 692 mV and 169 mV/dec for WTe2. Even though VTe2 has the lowest values in the exchange current density, the active site density, and turn-over-frequency (TOF) among the three TMTe2, the lowest charge transfer resistance (RCT) of VTe2 seems to be critical to achieving the best HER performance. First-principles calculations revealed that the basal-plane-active HER performance of metallic TMDs can be further enhanced with some Te vacancies. Our study paves the way to further study of the inherent catalytic activity of metallic 2D materials for active hydrogen production.

Boosted Electron-Transfer Kinetics of Hydrogen Evolution Reaction at Bimetallic RhCo Alloy Nanotubes in Acidic Solution

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co₂RhO₄ nanotubes. The reduction was conducted by thermal annealing of the Co₂RhO₄ nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO₄ solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm^-2 (-22 mV) and a small Tafel slope (-24.1 mV dec^-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.

Nanowire Genome: A Magic Toolbox for 1D Nanostructures

1D nanomaterials with high aspect ratio, i.e., nanowires and nanotubes, have inspired considerable research interest thanks to the fact that exotic physical and chemical properties emerge as their diameters approach or fall into certain length scales, such as the wavelength of light, the mean free path of phonons, the exciton Bohr radius, the critical size of magnetic domains, and the exciton diffusion length. On the basis of their components, aspect ratio, and properties, there may be imperceptible connections among hundreds of nanowires prepared by different strategies. Inspired by the heredity system in life, a new concept termed the "nanowire genome" is introduced here to clarify the relationships between hundreds of nanowires reported previously. As such, this approach will not only improve the tools incorporating the prior nanowires but also help to precisely synthesize new nanowires and even assist in the prediction on the properties of nanowires. Although the road from start-ups to maturity is long and fraught with challenges, the genetical syntheses of more than 200 kinds of nanostructures stemming from three mother nanowires (Te, Ag, and Cu) are summarized here to demonstrate the nanowire genome as a versatile toolbox. A summary and outlook on future challenges in this field are also presented.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.