Nanoporous Gold Films Research Articles

Ball-in-hole 3D nanoarchitectonics based on nanoporous Au film: Ultrasensitive, highly reliable, and reusable plasmonic platform

Hotspots have a locally enhanced electromagnetic field, effectively created by nanogaps in plasmonic metal nanostructures. The formation of uniform nanogaps, smaller than a few nanometers, allows for the detection of analytes at low concentrations and ensures reliable measurements across entire surface-enhanced Raman scattering (SERS) substrates. Despite the demand for SERS substrates in recent optical sensing applications, challenges remain in developing new techniques to maximize the number and optimize the size of nanogaps on large-area substrates. To address this issue, this study introduces a new ball-in-hole technique based on metal nanoarchitecture utilizing 3D nanoporous gold film (NPGF) and 0D gold nanoparticles (AuNPs). Using the ball-in-hole technique, 23 nm AuNPs are placed within the ∼ 28 nm mesopores of the metal film, creating uniform nanogaps of just a few nanometers that ensure consistent SERS signals across a large substrate area due to effective hotspots. The 23nmNP@NPGF substrate exhibited an enhancement factor (EF) of 1014 for 4-aminophenol (4-ATP), enabling detection at the attomole level. Moreover, the substrate retained its performance after five washing and reuse cycles, demonstrating excellent recyclability Finally, the substrate successfully detected femtomolar concentrations of key neurotransmitters like dopamine and glutamate, without requiring Raman reporters. This study presents a promising strategy for constructing metal nanoarchitectures with numerous hotspots, offering new possibilities for developing more efficient SERS substrates.

A Direct Dry Synthesis Route for High Purity Catalytic Nanoporous Metallic Films

Control of catalyst morphology is important because it affects many catalytic related properties such as, active sites, surface energy, and surface area, which can lead to tunable catalytic activity. Nanoporous metallic networks (NPMs), a morphology of interest for catalysis, contain many uncoordinated atoms at the surface and highly curved ligaments that can have a large effect on catalytic performance. Nanoporous self-supported metal structures have been synthesized in the past by dealloying of a master alloy,[1] which is a wet chemical method. This technique uses an Au-Ag alloy, from which Ag is etched away and which always results in NPMs containing residual amounts of the sacrificial metal (Ag) preventing the formation of high-purity structures. It follows that the catalytic properties of pure NPMs formed by dealloying can not be studied due to metal 'impurities' remaining in the structure. Although these 'impurities' contribute to catalytic activity and stability, it is difficult to control their amount and the systematic investigation of the 'impurity' effect is almost impossible for these NPMs.Here, we present results obtained by using physical vapor deposition, in the form of glancing angle deposition (GLAD), together with plasma etching to form nanoporous ultra-thin metal mesh structures, in a unique and facile dry synthesis method,[2] unlike most wet chemical synthesis methods used to prepare catalysts, which result chemical waste. The nanostructured metal mesh films are suitable for catalysis as they are extremely pure and highly porous, and contain high curvature ligaments, different crystal motifs, and many grain boundaries. We present nanoporous gold films (NPGF) prepared by our method as an example material. We show that the electrochemical structural stability of the NPGF is remarkably higher than that of dealloyed nanoporous gold, which is a result of the high amount of grain boundaries. Furthermore, the electrocatalytic performance of CH3OH oxidation is measured and the results show high catalytic activity for pure NPGF.[3] Our GLAD method can be applied to various metals and enables precise mixing or doping of different materials composing the NPMs. The high porosity, active sites, and potential elemental mixing will lead to new catalysts, especially suitable for CO2 reduction to fuels and value-added chemicals.[1] G. Wittstock, M. Bäumer, W. Dononelli, T. Klüner, L. Lührs, C. Mahr, L. V. Moskaleva, M. Oezaslan, T. Risse, A. Rosenauer, A. Staubitz, J. Weissmüller, A. Wittstock, Chem. Rev. 2023, 123, 6716.[2] H. Kwon, H.-N. Barad, A. R. Silva Olaya, M. Alarcón-Correa, K. Hahn, G. Richter, G. Wittstock, P. Fischer, ACS Appl. Mater. Interfaces 2023, 15, 5620.[3] H. Kwon, H.-N. Barad, A. R. Silva Olaya, M. Alarcón-Correa, K. Hahn, G. Richter, G. Wittstock, P. Fischer, ACS Catal. 2023, 11656.

Upcycling Compact Disks to Flexible Nanoporous Gold Electrodes for Nitrite Biosensing

Electrochemical biosensors are crucial in disease detection due to their simplicity, rapidity, and sensitivity. As a wearable or e-skin platform, electrochemical sensors are frequently restricted by gradual degradation, complexity, limited active surface area, arduous fabrication process, and high cost. Therefore, soft electrochemical biosensors that are mechanically biocompatible, easy to prototype, and robust for sensitive biosensing are highly sought. To mitigate such an issue, recordable compact disks (CDs) have been upcycled to advanced biosensors exhibiting flexible and disposable and being applicable to various biomedical applications, making them an economical and practical option. However, the limited surface area of the gold CDs electrode prevents optimal electrochemical catalytic performance. Nanostructure has been widely embedded in electrochemical biosensor construction to optimize electrode surface area and the number of active sites, which can contribute to improved detection sensitivity, selectivity, and electron transfer.Here, we aim to develop an advanced nanoporous gold film electrode (NPGFE) from CD for a simple, flexible, sensitive, and larger surface area electrode with reproducible areas. The fabrication and modification of gold CDs film were accomplished through two steps: 1) A mechanical cutter tailored the gold film after being transferred from CDs into a flexible substrate (Polyimide tape). Before placing the CDs film between the two laminating sheets, an aperture (1 mm diameter) was made in one of the laminating sheets to expose the tailored gold film electrode (GFE) and insulate the undesired area using a thermal laminator to ensure an adequate seal as a simple and low-cost approach; 2) The nanoporous gold (NPG) was electrochemically deposited onto the gold CDs film surface in gold (III) chloride trihydrate (HAuCl4·3H2O) and ammonium chloride (NH4Cl) solution at a potential of -4V for 100 s. Surface morphology characteristics and elemental analyses were investigated using scanning electron microscopy, while electrochemical studies were carried out in the CH Instruments potentiostat.The SEM images confirm a homogeneous distribution of NPG across the electrode’s surface. The energy-dispersive X-ray analyses exhibited the purity of the deposited NPG. The effective surface area was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 1 M KCl and 1 mM K3[Fe(CN)6] solution. From the slope of the Ip vs. v1/2 plot and the Randles-Sevcik equation, the active surface area of the NPGFE was significantly increased compared to the unmodified GFE. EIS was conducted to evaluate electron transfer resistance and obtain the semicircular diameter in Nyquist plots. In comparison to the unmodified GFE, the NPGFE showed a semicircle with a smaller diameter, indicating that the electron transfer resistance is minimized. The electrochemical characterization of the NPGFE was investigated by CV and amperometric techniques in 0.1 M PBS solution at ambient temperature (25°C) and pH 7.4. The NPGFE performance was studied at a fixed potential (0.77 V vs. Ag/AgCl) by analyzing the current response upon adding nitrite and anodic peak current at a potential range from 0.3 to 0.9 V (vs. Ag/AgCl). The calibration curve plot was linear over 0.5 μM to 9 mM with 20 nA·μM−1·cm−2 sensitivity and a low detection limit of 0.5 μM with a correlation coefficient (R2) of 0.99. The NPGFE's reproducibility reusability studies were conducted to evaluate electrode stability when prepared independently and utilized repeatedly under the same condition. Results demonstrate remarkable reproducibility and highly satisfactory reusability, making it suitable for practical application. The effect of pH on nitrite detection was investigated at different pH values. The anodic peak currents decreased and shifted to the low potential when the pH was increased from 5.0 to 10.0, indicating that protons were directly involved in the nitrite redox reaction. Also, the selectivity studies showed a significant increase in the current response when nitrite, ascorbic acid, and sodium sulfite were introduced to the solution, and there were no remarkable changes when other interferents were added. The long-term stability results showed that the NPGFE retains 99% of its initial current response to NO2 - after six months of storage, indicating satisfactory stability and long service life of NPGFE. Importantly, the sensing performance while stretching the NPGFE will be investigated to produce biocompatible relevant results.The flexible, nanoporous upcycled CDs electrode utilizing craft machines provide fast prototyping electrochemical biosensors for skin-interfaced bioelectronics. The nanoporous CD-based biosensor significantly improves electrocatalytic performance toward nitrite detection along with exceptional improvements in the cost-effective and sustainable fabrication process for flexible electronics. Future work relies on developing system-integrated biosensors based on systematic reliability and feasibility tests. Soft upcycled bioelectronics holds significant potential in advancing biomedical in situ real-time analysis in various platforms of flexible and nanostructured biosensors. Figure 1

A hybrid effective medium description for nanoporous gold films and thickness-mediated control of optical absorption.

With the increasing demand for sensing platforms operating across UV, visible, and near-infrared wavelengths, nanoporous gold has emerged as an ideal substrate for rapid, quantitative detection of analytes with excellent specificity and high sensitivity. This study investigates thickness-mediated compositional changes and their impact on scattering characteristics of thin nanoporous gold films fabricated using selective chemical etching. Specifically, we observe thickness-induced morphological and structural changes across different fabricated samples from 25 to 100 nm in thickness. Upon their optical characterization across UV-VIS-NIR spectral regime, we notice that the constitutional differences among samples manifest distinctively & deterministically in their total optical scattering response. In order to gain insights into these observed scattering responses and to fathom the subtle connections between structural properties of NPG films and their optical response, a hybrid theoretical model comprising Maxwell-Garnett & Bruggeman effective medium approximations has been adopted. Our approach not only allows to appropriately account for the inhomogeneous nature of these films, but also corroborates well with the atomic force microscopy characterizations of the fabricated samples. Furthermore, tracing such a theoretical model is important as it helps in systematically ascertaining additional loss terms emerging in the complex dielectric function of films due to their nanoscale porosity & roughness, permitting a good reproduction of measured optical spectra. We believe, our approach will not only facilitate accurate regulation of losses in NPG thin films but will also aid in deriving customized optical performance from them, thereby advancing their potential applications in sensing and beyond.

Flexible Graphene Paper Modified Using Pt&Pd Alloy Nanoparticles Decorated Nanoporous Gold Support for the Electrochemical Sensing of Small Molecular Biomarkers.

The exploration into nanomaterial-based nonenzymatic biosensors with superb performance in terms of good sensitivity and anti-interference ability in disease marker monitoring has always attained undoubted priority in sensing systems. In this work, we report the design and synthesis of a highly active nanocatalyst, i.e., palladium and platinum nanoparticles (Pt&Pd-NPs) decorated ultrathin nanoporous gold (NPG) film, which is modified on a homemade graphene paper (GP) to develop a high-performance freestanding and flexible nanohybrid electrode. Owing to the structural characteristics the robust GP electrode substrate, and high electrochemically catalytic activities and durability of the permeable NPG support and ultrafine and high-density Pt&Pd-NPs on it, the resultant Pt&Pd-NPs-NPG/GP electrode exhibits excellent sensing performance of low detection limitation, high sensitivity and anti-interference capability, good reproducibility and long-term stability for the detection of small molecular biomarkers hydrogen peroxide (H2O2) and glucose (Glu), and has been applied to the monitoring of H2O2 in different types of live cells and Glu in body fluids such as urine and fingertip blood, which is of great significance for the clinical diagnosis and prognosis in point-of-care testing.

Characterization of ultrathin nanoporous gold films for improving the performance of SPR biochemical sensors

Surface plasmon resonance biochemical sensors with an ultra-thin nanoporous gold film.

Self-Detachment of Nanoporous Thin Films

Nanoporous metals consist of a network of interconnected ligaments with diameters tunable between 5 and 500 nm. The talk focusses on nanoporous metal thin films prepared by electrochemical dealloying of 300 nm thick Au25Ag75 films deposited on a pure Au base layer. This type of nanoporous gold film is the subject of many studies investigating the material as sensor, as catalyst, or as substrate for energy storage.The massive Au base layer is intended as an adhesion promoter and to prevent the corrosion from attacking the substrate. Yet, contrary to expectation, we observed that the as-dealloyed nanoporous films developed a gap near the base layer, with extremely loose connection. Screening electron micrographs in earlier publications revealed that the deficit in connectivity is ubiquitous – even though it has not been broached. We could readily reproduce the feature in kinetic Monte Carlo simulations of dealloying, with no special assumptions on the processes near the base layer. The talk will describe these observations, and we argue that the evolution of the connectivity in nanoporous thin films is sensitive to gradients, in the direction of the film thickness, of the laterally averaged surface mean curvature. Specifically, surface diffusion driven by the energetically favorable planar substrate results in a net current from ligaments connected to the substrate towards the substrate, leading to degradation and eventual pinch-off of these ligaments. A similar phenomenon occurs at the outer surface, causing densification and retraction of the outermost ligaments.Our findings suggest that this phenomenon may be relevant for all nanoscopic contact interfaces where surface diffusion is sufficiently fast. These results have significant implications for the design and implementation of nanoporous thin films in various applications, including sensor and actuator devices. Mitigation strategies will be discussed.Reference:G. Henkelmann, D. Waldow, M. Liu, L. Lührs, Y. Li and J. Weissmüller; Self-Detachment and Subsurface Densification of Dealloyed Nanoporous Thin Films. Nano Lett 22 (2022) 6787. Figure 1

Hydrogen sensing capabilities of highly nanoporous black gold films

Hydrogen sensing is a crucial topic for many industrial and environmental applications regarding the green deal and the use of hydrogen as a next-generation energy source/energy-storage medium. Therefore, many different approaches are being used to find sensitive, reliable and inexpensive devices for hydrogen detection. One such approach is the use of chemiresistive nanostructured materials that provide a large surface area for hydrogen adsorption. In this paper, we present a detailed study of the hydrogen sensing capabilities of highly nanoporous black gold films that show fast response and recovery times (0.5 min) while operating at low temperatures (40 °C). To investigate the sensing properties of black gold, films with different levels of nanoporosity were prepared and tested to a hydrogen concentration in the range of 0.25–0.95 %. Film morphology was characterised by AFM, SEM and XPS. To correctly examine the nanopores and defects in prepared films, Variable Energy Positron Annihilation Spectroscopy (VEPAS) was used. We found that nanoporous black gold is suitable as an active layer of chemiresistor for hydrogen sensing and that its sensitivity is the function of the film nanoporosity. Possible mechanisms of hydrogen-gold interactions are discussed.

Ultra-Pure Nanoporous Gold Films for Electrocatalysis

Ultra-Pure Nanoporous Gold Films for Electrocatalysis

Study on a nano-porous gold/polyamidoamine (NPG/PAMAM)-based electrochemical aptamer biosensor for the detection of ochratoxin a in the red wine

In this study, a novel electrochemical aptamer sensor for detecting ochratoxin A (OTA) was constructed. First, a gold-copper alloy film was prepared via electrochemical deposition, and copper was selectively dissolved in constant potential mode for obtaining the nano-porous gold modified screen-printed carbon electrodes (NPG/SPCE). Then, 2-mercaptoethylamine was dropped on the NPG/SPCE surface and Au-S covalent bonds were formed for immobilizing the metal. Glutaraldehyde as cross-linking agent was added, which resulted in immobilization and attachment of PAMAM to the 2-mercaptoethylamine through the dehydration condensation reaction. During the preparation process, the nano-porous gold and PAMAM-modified layers were characterized by SEM, XRD, and IR spectroscopy, respectively. The characterization results showed that the nano-porous gold and PAMAM composite films were successfully modified. Finally, the OTA aptamer was cross-linked with PAMAM by glutaraldehyde to complete construction of the Apt/PAMAM/NPG/SPCE sensor. The electrochemical performance of this sensor was tested in ochratoxin A solutions with the DPV method. The results showed that the sensor’s reproducibility, stability, and specificity were good. The spiked recoveries in red wine ranged from 99.65%∼101.6%, with a linear range of 0.5 ng/mL∼20 ng/mL and a minimum detection limit of 0.141 ng/mL. Thus, the novel biosensor may provide a promising tool for the trace detection of OTA.

Guided Wrinkling of Hierarchically Structured Nanoporous Gold Films for Improved Surface‐Enhanced Raman Scattering Performance (Adv. Mater. Interfaces 18/2023)

Guided Wrinkling of Hierarchically Structured Nanoporous Gold Films for Improved Surface‐Enhanced Raman Scattering Performance (Adv. Mater. Interfaces 18/2023)

Guided Wrinkling of Hierarchically Structured Nanoporous Gold Films for Improved Surface‐Enhanced Raman Scattering Performance

AbstractPlasmonic nanostructured metals have many advantages for applications in high‐performance surface‐enhanced Raman scattering (SERS) spectroscopy. In particular, unique designing nanostructures with bicontinuous ligaments surrounded by cylindrical voids with tunable dense pores from a few to hundreds of nanometers can be utilized for the high‐performance SERS‐active substrate. Here, a fabrication strategy is reported to prepare hierarchically arranged micro/nanostructures of wrinkled nanoporous gold (WNPG) films, which involves laminating of the dealloyed Au film on the heat‐shrinkable shape‐memory polymer film and geometrical modulation of the substrate. As a result, the various types of WNPG films are crafted with a remarkable density of cracks in the structured surface area. Specifically, the WNPG films consisting of multilayered overlapping features are explored and used as the SERS‐active substrate. This dual porosity coupled with localized surface plasmon resonance estimated by numerical simulation in a suitable model of bicontinuous ligaments is found to be the core mechanism for the enhancement of SERS sensitivity, which quantitatively characterizes the “hot spots” from the surface to interlayers. These suggested characteristic features are fully assessed by applying a series of dye molecules and DNA strands on the prepared SERS substrate, demonstrating the enhanced intensity of the Raman scattering signals on the optimized WNPG surface.

Elucidating Mass Transport within Nanoporous Au for CO2 Electroreduction

The electrochemical reduction of CO2 to value-added chemicals renewable electricity is a promising and ecofriendly strategy to achieve the national strategic goal of “carbon peak and carbon neutrality” and solve the greenhouse effect. Due to the variety of products in CO2 electroreduction (CO2ER), catalytic selectivity has become a key factor in the design of electrode structure. Herein, a systematic investigation of CO2ER on the nanoporous gold films with different thicknesses prepared by the self-deposition method developed by ourselves. Mass transfer effects are found to play an important role in determining product selectivity and activity. The specific activity for CO evolution (jCO) with exponential declination has more dramatic tendency than the specific activity for hydrogen evolution (jH2) with linear decay with increasing nanoporous gold film thickness. Different from the behaviors within the mesoporous structures in previous studies, the retarded transport of HCO3− ions within the nanoscale pores is more sensitive than that of protons. This phenomenon implies the necessity of considering mass transfer effects in the design of outstanding electrocatalysts for CO2ER as well as for understanding the geometrical infrastructure-performance relationships.

Enhanced Photothermal Steam Generation and Gold Using the Efficiency of Ultralight Gold Foam with Hierarchical Porosity

Controlling the optical properties of metal plasma nanomaterials through structure manipulation has attracted great attention for solar steam generation. However, realizing broadband solar absorption for high-efficiency vapor generation is still challenging. In this work, a free-standing ultralight gold film/foam with a hierarchical porous microstructure and high porosity is obtained through controllably etching a designed cold-rolled (NiCoFeCr)99Au1 high-entropy precursor alloy with a unique grain texture. During chemical dealloying, the high-entropy precursor went through anisotropic contraction, resulting in a larger surface area compared with that from the Cu99Au1 precursor although the volume shrinkage is similar (over 85%), which is beneficial for the photothermal conversion. The low Au content also results in a special hierarchical lamellar microstructure with both micropores and nanopores within each lamella, which significantly broadens the optical absorption range and makes the optical absorption of the porous film reach 71.1-94.6% between 250 and 2500 nm. In addition, the free-standing nanoporous gold film has excellent hydrophilicity, with the contact angle reaching zero within 2.2 s. Thus, the 28 h dealloyed nanoporous gold film (NPG-28) exhibits a rapid evaporation rate of seawater under 1 kW m-2 light intensity, reaching 1.53 kg m-2 h-1, and the photothermal conversion efficiency reaches 96.28%. This work demonstrates the enhanced noble metal gold using efficiency and solar thermal conversion efficiency by controlled anisotropic shrinkage and forming a hierarchical porous foam.

A nanoporous gold film sensor modified with polypyrrole/CuO nanocomposite for electrochemical determination of piroxicam and tramadole

In this paper, an electrochemical sensor was developed to determine piroxicam (PX) and tramadole (Tr) based on their enhanced electrochemical responses at the surface of the polypyrrole/CuO nanocomposite-modified nanoporous gold film (NPGF) electrode. The experimental results showed that PX provide an oxidation peak at 0.65 V in pH = 8.0. The DPV results were linearly affiliated on PX concentration within the two closed windows (C1PX = 0.05–30.0 μM, correlation coefficient of 0.9905, and C2PX = 50.0–300.0 μM, correlation coefficient of 0.9927). From voltammetric curves, the detection limit (LOD = 3Sb/m) for PX at a surface of PPY-CuO-NPGF electrode was appeared to be 0.01 μM. Furthermore, the ability of PPY-CuO-NPGF electrode for simultaneous measurement of PX and Tr was investigated. The suggested sensor shows a long-time stability, good repeatability, and rapid response in the mixture media of PX and Tr.

Detection of hot electron-driven photochemical reaction of steady- state NO2 gas molecules by surface–enhanced Raman spectroscopy

In this work, a steady-state detection method of 50 ppm of nitrogen dioxide NO2 gas in a polyethylene (PET) bag using surface-enhanced Raman spectroscopy (SERS) is reported for the first time. SERS was performed on different shapes of gold nanostructures, gold nanostars (GNS) and nanoporous gold film (NPG). In both, the vibrational modes assigned to the adsorbents of NO2 molecules such as NO2, NO, NO−3, N2O3, and N2O5 were detected. The generation of adsorbents is due to the photo-chemical reaction driven by the hot electrons generated at the surface of gold nanostructures. Our finding is supported by a finite element simulation excluding the plasmon-induced photo-thermal process due to the long duration of excitation compared to the duration of SERS measurement. The mechanism of NO2 photochemical reactions is explained, confirming the adsorption of NO2 molecules on the gold surface towards their oxygen atoms.

Surface plasmon resonance gas sensor with a nanoporous gold film

This work demonstrates an optical gas sensor based on the surface plasmon resonance (SPR) of nanoporous gold (NPG) thin films. The NPG films are prepared by a sputtering-dealloying combined method, and they can support the propagating surface plasmon mode and adsorb a large number of gaseous molecules; the interaction of the internal plasmon field and the adsorbed molecules enables the NPG-SPR sensor to have high sensitivity. The Kretschmann-type spectral NPG-SPR sensor is fabricated with a 60-nm-thick NPG film, and its spectral response to toxic H2S gas was investigated at room temperature. The optimal sensitivity of the sensor to H2S was achieved by controlling the dealloying time to tune the film porosity. Comparison of the spectral sensitivity to 100 ppm H2S indicates that the NPG-SPR sensor is at least six times more sensitive than a conventional Au-SPR sensor.

Use of a nano-porous gold film electrode modified with chitosan / polypyrrole for electrochemical determination of metronidazole in the Presence of Acetaminophen

This study, it was aimed to provide a sensitive, easy and selective method for designing Nano-porous gold film electrode (NPGF) electrode for simultaneous measurement of metronidazole (MT) and acetaminophen (AC). For this purpose, the NPGF electrode surface was modified with chitosan (CS) and poly pyrrole (PPY) by electrochemical method, and then CS and PPY modified NPGF (PPY-CS-NPGF) electrode were used to measure these drugs. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are employed for the characterization of the attained PPY-CS-NPGF electrode. Using cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and chronoamperometry, the electrochemical behavior of MT was investigated with the modified electrode. By differential pulse voltammetry, linear ranges of concentration 0.005–100 μM with linear coefficients of 0.9898 and a detection limit of 0.0009 μM were obtained for MT. Finally, an electrochemical sensor was used to measure MT in a real sample, which yielded acceptable results. PPY-CS-NPGF electrodes have a wide linear range, high selectivity, sensitivity and stability and can be used successfully to determine these drugs.

Designing independent water transport channels to improve water flooding in ultra-thin nanoporous film cathodes for PEMFCs

Utilization of 3D nanostructured Pt cathodes could obviously improve performances of proton exchange membrane fuel cells (PEMFCs) owing to the reduced tortuosity and the bi-continuous nanoporous structure. However, these cathodes usually suffer from the flooding problem ascribed to the ionomer-free and nanoscale pores which are more susceptible to water condensation. In this paper, ultra-thin nanoporous metal films (100 nm) were utilized to construct PEMFC cathodes and independent transport channels were designed separately for water and gas aiming at the flooding problem. Nanoporous gold (NPG) film was used as the model support for loading Pt nanoparticles owing to its controllable and stable structure. After optimizing the polytetrafluoroethylene (PTFE) content and carbon loading in the gas diffusion layer (GDL), plasma treatment under O2 atmosphere was used to pattern the GDL with independent water transport channels. The obtained liquid permeation coefficients and oxygen gains demonstrated the obviously improved water and O2 transport. By using a home-made optimized GDL and a nanoporous film cathode with pore size ∼60 nm, the flooding problem could be facilely solved. With a Pt loading of ∼16 μg cm−2, this 3D nanostructured cathode exhibits a PEMFC performance of ∼957 mW cm−2 at 80 °C. The Pt power efficiency is about 4 times higher than that of the commercial Pt/C cathode (50 μg cm−2, 756 mW cm−2). Obviously, this study provides a simple but effective methodology to solve the water flooding problem in the ultra-thin nanoporous film cathodes which is applicable for other types of 3D nanostructured PEMFC cathodes.

A facile electrochemical method for rapid determination of 3-chloropropane-1,2-diol in soy sauce based on nanoporous gold capped with molecularly imprinted polymer

3-monochloropropane-1,2-diol (3-MCPD) is a well-known heat-produced food contaminant, which has been reported to be carcinogenic, nephrotoxic, and reproductively toxic. In this study, a facile electrochemical sensor based on nanoporous gold (NPG) capped with molecularly imprinted polymer (MIP) was constructed for the rapid and selective determination of 3-monochloropropane-1,2-diol (3-MCPD). Firstly, NPG was fabricated on the electrode through coating the glass carbon electrode (GCE) surface with NPG film to provide an ideal substrate for polymerization of the MIP membrane and improve the electrocatalysis activity of the sensor. Then, the MIP membrane was constructed on the NPG surface via self-assembly by electropolymerization to realize selective recognition of target 3-MCPD molecules. As a consequence of the combined effect of NPG and MIP, the optimized molecularly imprinted polymer/nanoporous gold/glassy carbon electrode (MIP/NPG/GCE) sensor exhibited outstanding analytical performance towards 3-MCPD with a much wider linear range from 10 −16 to 10 −7 mol/L and fairly low detection limit of 3.5 × 10 −17 mol/L (S/N = 3). Meanwhile, the constructed electrochemical sensor presented outstanding specificity, anti-interference capability, and reproducibility. In order to demonstrate practical applicability, the MIP/NPG/GCE was applied for the detection of 3-MCPD in real soy sauce and satisfactory results were obtained with recovery rates ranging from 105.90% to 107.52%. • An electrochemical sensor was prepared for detecting 3-MCPD using NPG and MIP. • NPG improved the electrocatalysis activity of the sensor. • The structure of NPG provided an ideal substrate for polymerization of MIP film. • The MIP film self-assembled on NPG realized selective recognition of 3-MCPD. • The fabricated sensor showed outstanding analytical performance towards 3-MCPD.