Tailoring the Interfacial Interactions of van der Waals 1T-MoS2/C60 Heterostructures for High-Performance Hydrogen Evolution Reaction Electrocatalysis

N-Doped Graphene as an Efficient Metal-Free Electrocatalyst for Indirect Nitrate Reduction Reaction

N-doped graphene samples with different N species contents were prepared by a two-step synthesis method and evaluated as electrocatalysts for the nitrate reduction reaction (NORR) for the first time. In an acidic solution with a saturated calomel electrode as reference, the pyridinic-N dominant sample (NGR2) had an onset of 0.932 V and a half-wave potential of 0.833 V, showing the superior activity towards the NORR compared to the pyrrolic-N dominant N-doped graphene (onset potential: 0.850 V, half-wave potential: 0.732 V) and the pure graphene (onset potential: 0.698 V, half-wave potential: 0.506 V). N doping could significantly boost the NORR performance of N-doped graphene, especially the contribution of pyridinic-N. Density functional theory calculation revealed the pyridinic-N facilitated the desorption of NO, which was kinetically involved in the process of the NORR. The findings of this work would be valuable for the development of metal-free NORR electrocatalysts.

Engineering of Electron Affinity and Interfacial Charge Transfer of Graphene for Self-Powered Nonenzymatic Biosensor Applications

Facile electron transport and intimate electronic contact at the catalyst-electrode interface are critical for the ideal performance of electrochemical devices such as glucose biofuel cells and biosensors. Here, through a comprehensive experimental-theoretical exploration, we demonstrate that engineering of interfacial properties, including interfacial electron dynamics, electron affinity, electrode-catalyst-adsorbate electrical synergy, and electrocatalytically active surface area, can lead to highly efficient graphene-based electrochemical devices. We selected two closely related but electronically and surface chemically different functionalized graphene analogues-graphene acid (GA) and reduced graphene oxide (rGO)-as the model graphenic platforms. Our studies reveal that compared to rGO, GA is a superior bifunctional catalyst with high oxygen reduction reaction (an onset potential of 0.8 V) and good glucose oxidation activities. Spectroscopic and electrochemical analysis of GA and rGO indicated that the higher carboxylic acid content on GA increases its overall electron affinity and coupled with improved conductivity and band alignment, which leads to GA's better electrochemical performance. The formulation of a heterostructure between GA and samarium oxide (Sm₂O₃) nanoparticles led to augmented conductivity (lower charge-transfer resistance) and glucose binding affinity, resulting in a further enhanced glucose oxidation activity. The interdimensional Sm₂O₃/GA heterostructure, leveraging their enhanced glucose oxidation capacity, exhibited excellent nonenzymatic amperometric glucose sensing performance, with a detection limit of 107 nM and a sensitivity of 20.8 μA/μM. Further, a nonenzymatic, membrane-free glucose biofuel cell (with Sm₂O₃/GA heterostructure as anode and GA as biocathode) produced a power density of 3.2 μW·cm^-2 (in PBS spiked with 3 mM glucose), which can function as self-powered glucose sensors with 70 nM limit of detection. The study establishes the potential of interfacial engineering of GA to engage it as a highly tunable substrate for a broad range of electrochemical applications, especially in future self-powered biosensors.

Recent Advances on Transition Metal Dichalcogenides for Electrochemical Energy Conversion

Transition metal dichalcogenides (TMDCs) hold great promise for electrochemical energy conversion technologies in view of their unique structural features associated with the layered structure and ultrathin thickness. Because the inert basal plane accounts for the majority of a TMDC's bulk, activation of the basal plane sites is necessary to fully exploit the intrinsic potential of TMDCs. Here, recent advances on TMDCs-based hybrids/composites with greatly enhanced electrochemical activity are reviewed. After a summary of the synthesis of TMDCs with different sizes and morphologies, comprehensive in-plane activation strategies are described in detail, mainly including in-plane-modification-induced phase transformation, surface-layer modulation, and interlayer modification/coupling. Simultaneously, the underlying mechanisms for improved electrochemical activities are highlighted. Finally, the strategic evaluation on further research directions of TMDCs in-plane activation is featured. This work would shed some light on future design trends of TMDCs-based functional materials for electrochemical energy-related applications.

Van der Waals Heterostructures-Recent Progress in Electrode Materials for Clean Energy Applications

The unique layered morphology of van der Waals (vdW) heterostructures give rise to a blended set of electrochemical properties from the 2D sheet components. Herein an overview of their potential in energy storage systems in place of precious metals is conducted. The most recent progress on vdW electrocatalysis covering the last three years of research is evaluated, with an emphasis on their catalytic activity towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). This analysis is conducted in pair with the most active Pt-based commercial catalyst currently utilized in energy systems that rely on the above-listed electrochemistry (metal-air battery, fuel cells, and water electrolyzers). Based on current progress in HER catalysis that employs vdW materials, several recommendations can be stated. First, stacking of the two types vdW materials, with one being graphene or its doped derivatives, results in significantly improved HER activity. The second important recommendation is to take advantage of an electronic coupling when stacking 2D materials with the metallic surface. This significantly reduces the face-to-face contact resistance and thus improves the electron transfer from the metallic surface to the vdW catalytic plane. A dual advantage can be achieved from combining the vdW heterostructure with metals containing an excess of d electrons (e.g., gold). Despite these recent and promising discoveries, more studies are needed to solve the complexity of the mechanism of HER reaction, in particular with respect to the electron coupling effects (metal/vdW combinations). In addition, more affordable synthetic pathways allowing for a well-controlled confined HER catalysis are emerging areas.

1T-Phase Dirac Semimetal PdTe2 Nanoparticles for Efficient Photothermal Therapy in the NIR-II Biowindow

1T-phase transition-metal dichalcogenides (TMDs) nanomaterials are one type of emerging and promising near-infrared II (NIR-II) photothermal agents (PTAs) derived from their distinct metallic electronic structure, but it is still challenging to synthesize these nanomaterials. Herein, PdTe2 nanoparticles (PTNs) with a 1T crystal symmetry and around 50 nm in size are prepared by an electrochemical exfoliation method, and the corresponding photothermal performances irradiated under a NIR-II laser have been explored. The encapsulation of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG) endows PTNs with water solubility, enhanced photothermal stability, and high biocompatibility. Notably, PTN/DSPE-PEG displays a potent absorbance through the NIR-II zone and considerable photothermal conversion efficiency, which is up to 68% when irradiated with a 1060 nm laser. With these unique photothermal properties, excellent in vitro and in vivo tumor inhibition effects of PTN/DSPE-PEG have been achieved under the irradiation of a NIR-II (1060 nm) laser without visible toxicity to normal tissues, suggesting that it is an efficient NIR-II photothermal nanoagent.

A New Class of Molecular Electrocatalysts for Hydrogen Evolution: Catalytic Activity of M3N@C2n (2n = 68, 78, and 80) Fullerenes

The electrocatalytic properties of some endohedral fullerenes for hydrogen evolution reactions (HER) were recently predicted by DFT calculations. Nonetheless, the experimental catalytic performance under realistic electrochemical environments of these 0D-nanomaterials have not been explored. Here, for the first time, we disclose the HER electrocatalytic behavior of seven M₃N@2n (2n = 68, 78, and 80) fullerenes (Gd₃N@I_h(7)-C₈₀, Y₃N@I_h(7)-C₈₀, Lu₃N@I_h(7)-C₈₀, Sc₃N@I_h(7)-C₈₀, Sc₃N@D_5h(6)-C₈₀, Sc₃N@D_3h(5)-C₇₈, and Sc₃N@D₃(6140)-C₆₈) using a combination of experimental and theoretical techniques. The non-IPR Sc₃N@D₃(6140)-C₆₈ compound exhibited the best catalytic performance toward the generation of molecular hydrogen, exhibiting an onset potential of -38 mV vs RHE, a very high mass activity of 1.75 A·mg^-1 at -0.4 V vs RHE, and an excellent electrochemical stability, retaining 96% of the initial current after 24 h. The superior performance was explained on the basis of the fused pentagon rings, which represent a new and promising HER catalytic motif.

Hybrid Hierarchical Heterostructures of Nanoceramic Phosphors as Imaging Agents for Multiplexing and Living Cancer Cells Translocation

Existing fluorescent labels used in life sciences are based on organic compounds with limited lifetime or on quantum dots which are either expensive or toxic and have low kinetic stability in biological environments. To address these challenges, luminescent nanomaterials have been conceived as hierarchical, core–shell structures with spherical morphology and highly controlled dimensions. These tailor-made nanophosphors incorporate Ln:YVO₄ nanoparticles (Ln = Eu(III) and Er(III)) as 50 nm cores and display intense and narrow emission maxima centered at ∼565 nm. These cores can be encapsulated in silica shells with highly controlled dimensions as well as functionalized with chitosan or PEG5000 to reduce nonspecific interactions with biomolecules in living cells. Confocal fluorescence microscopy in living prostate cancer cells confirmed the potential of these platforms to overcome the disadvantages of commercial fluorophores and their feasibility as labels for multiplexing, biosensing, and imaging in life science assays.

Tuning the Intermolecular Electron Transfer of Low-Dimensional and Metal-Free BCN/C60 Electrocatalysts via Interfacial Defects for Efficient Hydrogen and Oxygen Electrochemistry

The development of low-dimensional (LD) supramolecular materials with multifunctional electrocatalytic properties has sparked the attention of the catalysis community. Herein, we report the synthesis of a new class of 0D-2D heterostructures composed of boron carbon nitride nanosheets (BCN NSs) and fullerene molecules (C₆₀/F) that exhibit multifunctional electrocatalytic properties for the hydrogen evolution/oxidation reactions (HER/HOR) and the oxygen evolution/reduction reactions (OER/ORR). The electrocatalytic properties were studied with varying F:BCN weight ratios to optimize the intermolecular electron transfer (ET) from the BCN NSs to the electron-accepting C₆₀ molecules. The nanohybrid supramolecular material with 10 wt % F in BCN NSs (10% F/BCN) exhibited the largest Raman and C 1s binding energy shifts, which were associated with greater cooperativity interactions and enhanced ET processes at the F/BCN interface. This synergistic interfacial phenomenon resulted in highly active catalytic sites that markedly boosted electrocatalytic activity of the material. The 10% F/BCN showed the highest tetrafunctional catalytic performance, outperforming the OER catalytic activity of commercial RuO₂ catalysts with a η₁₀ of 390 mV and very competitive onset potential values of -0.042 and 0.92 V vs RHE for HER and ORR, respectively, and a current density value of 1.47 mA cm^-2 at 0.1 V vs RHE with an ultralow ΔG_H* value of -0.03 eV toward the HOR process. Additionally, the 10% F/BCN catalyst was also used as both cathode and anode in a water splitting device, delivering a cell potential of 1.61 V to reach a current density of 10 mA cm^-2.