H2 quantification based on selective pre-concentration and oxidative stripping at Pd modified microelectrodes

Quantitative Measurements of Electrocatalytic Reaction Rates with NanoSECM

Scanning electrochemical microscopy (SECM) has been extensively used for mapping electrocatalytic surface reactivity; however, most of the studies were carried out using micrometer-sized tips, and no quantitative kinetic experiments on the nanoscale have yet been reported to date. As the diffusion-limited current density at a nanometer-sized electrode is very high, an inner-sphere electron-transfer process occurring at a nanotip typically produces a kinetic current at any attainable overpotential. Here, we develop a theory for substrate generation/tip collection (SG/TC) and feedback modes of SECM with a kinetic tip current and use it to evaluate the rates of hydrogen and oxygen evolution reactions in a neutral aqueous solution from the current-distance curves. The possibility of using chemically modified nanotips for kinetic measurements is also demonstrated. The effect of the substrate size on the shape of the current-distance curves in SG/TC mode SECM experiments is discussed.

Pt-Black-Modified (Hemi)spherical AFM Sensors: In Situ Imaging of Light-Driven Hydrogen Peroxide Evolution

In this work, we present (hemi)spherical atomic force microscopy (AFM) sensors for the detection of hydrogen peroxide. Platinum-black (Pt-B) was electrodeposited onto conductive colloidal AFM probes or directly at recessed microelectrodes located at the end of a tipless cantilever, resulting in electrocatalytically active cantilever-based sensors that have a small geometric area but, due to the porosity of the films, exhibit a large electroactive surface area. Focused ion beam-scanning electron microscopy tomography revealed the porous 3D structure of the deposited Pt-B. Given the accurate positioning capability of AFM, these probes are suitable for local in situ sensing of hydrogen peroxide and at the same time can be used for (electrochemical) force spectroscopy measurements. Detection limits for hydrogen peroxide in the nanomolar range (LOD = 68 ± 7 nM) were obtained. Stability test and first in situ proof-of-principle experiments to achieve the electrochemical imaging of hydrogen peroxide generated at a microelectrode and at photocatalytically active structured poly(heptazine imide) films are demonstrated. Force spectroscopic data of the photocatalyst films were recorded in ambient conditions, in solution, and by applying a potential, which demonstrates the versatility of these novel Pt-B-modified spherical AFM probes.

Integrated CuO/Pd Nanospike Hydrogen Sensor on Silicon Substrate

A large area of randomly distributed nanospike as nanostructured template was induced by femtosecond (fs) laser on a silicon substrate in water. Copper oxide (CuO) and palladium (Pd) heterostructured nanofilm were coated on the nanospikes by magnetron sputtering technology and vacuum thermal evaporation coating technology respectively for the construction of a p-type hydrogen sensor. Compared with the conventional gas sensor based on CuO working at high temperature, nanostructured CuO/Pd heterostructure exhibited promising detection capability to hydrogen at room temperature. The detection sensitivity to 1% H₂ was 10.8%, the response time was 198 s, and the detection limit was as low as 40 ppm, presenting an important application prospect in the clean energy field. The excellent reusability and selectivity of the CuO/Pd heterostructure sensor toward H₂ at room temperature were also demonstrated by a series of cyclic response characteristics. It is believed that our room-temperature hydrogen sensor fabricated with a waste-free green process, directly on silicon substrate, would greatly promote the future fabrication of a circuit-chip integrating hydrogen sensor.

Cobaloxime Complex Salts: Synthesis, Patterning on Carbon Nanomembranes and Heterogeneous Hydrogen Evolution Studies

Cobaloximes are promising, earth‐abundant catalysts for the light‐driven hydrogen evolution reaction (HER). Typically, these cobalt(III) complexes are prepared in situ or employed in their neutral form, for example, [Co(dmgH)₂(py)Cl], even though related complex salts have been reported previously and could, in principle, offer improved catalytic activity as well as more efficient immobilization on solid support. Herein, we report an interdisciplinary investigation into complex salts [Co(dmgH)₂(py)₂]⁺[Co(dmgBPh₂)₂Cl₂]⁻, TBA+[Co(dmgBPh2)2Cl2]- and [Co(dmgH)₂(py)₂]⁺BArF⁻. We describe their strategic syntheses from the commercially available complex [Co(dmgH)₂(py)Cl] and demonstrate that these double and single complex salts are potent catalysts for the light‐driven HER. We also show that scanning electrochemical cell microscopy can be used to deposit arrays of catalysts [Co(dmgH)₂(py)₂]⁺[Co(dmgBPh₂)₂Cl₂]⁻, TBA+[Co(dmgBPh2)2Cl2]- and [Co(dmgH)₂(py)Cl] on supported and free‐standing amino‐terminated ∼1‐nm‐thick carbon nanomembranes (CNMs). Photocatalytic H₂ evolution at such arrays was quantified with Pd microsensors by scanning electrochemical microscopy, thus providing a new approach for catalytic evaluation and opening up novel routes for the creation and analysis of “designer catalyst arrays”, nanoprinted in a desired pattern on a solid support.