High Electrochemical Active Surface Area Research Articles

Novel 3-D urchin-like Ni– Co–W porous nanostructure as efficient bifunctional superhydrophilic electrocatalyst for both hydrogen and oxygen evolution reactions

Fabrication of an electrocatalyst with remarkable electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important for the production of hydrogen energy. In this study, Ni–Co–W alloy urchin-like nanostructures were fabricated by binder-free and cost-effective electrochemical deposition method at different applied current densities and HER and OER electrocatalytic activity was studied. The results of this study showed that the microstructure and morphology are strongly influenced by the electrochemical deposition parameters and the best electrocatalytic properties are obtained at the electrode created at the 20 mA.cm−2applied current density. The optimum electrode requires −66 mV and 264 mV, respectively, for OER and HER reactions for delivering the 10 mA cm−2 current density. The optimum electrode also showed negligible potential change after 10 h electrolysis at 100 mA cm−2, which means remarkable electrocatalytic stability. In addition, when this electrode used as a for full water splitting, it required only 1.58 V to create a current density of 10 mA cm−2. Such excellent electrocatalytic activity and stability can be related to the high electrochemical active surface area, being binder-free, high intrinsic electrocatalytic activity and hydrophilicity. This study introduces a simple and cost-effective method for fabricating of effective electrodes with high electrocatalytic activity.

Shape-control synthesis of PdCu nanoparticles with excellent catalytic activities for direct alcohol fuel cells application

In this article, we described a simple method of PdCu nanoparticles (NPs) synthesis in different morphologies at 120 °C using polyvinylpyrrolidone (PVP) capping agent and ethylene glycol (EG) solvent. Form instrumental characterization it is find out that PdCu NPs are prepared in different morphologies by varying the Pd:Cu weight percent (wt.%) ratios. Nanospheres (NS) are obtained in the absence of Cu, sphere-like NPs having Pd3Cu1 composition are obtained at 3:1 wt.% ratio, cubic NPs having Pd1Cu1 composition are obtained at 1:1 wt.% ratio and cube-like NPs having Pd1Cu3 composition are obtained at 1:3 wt.% ratio. The metals wt.% ratio not only controlled the morphology, but also affected the catalytic activity toward methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) in alkaline media. The PdCu catalyst, in 1:1 wt.% ratio, have demonstrated high specific and mass activities toward MOR (18.07 mA cm−2 and 11.15 A mgPd−1) and EOR (10.24 mA cm−2 and 6.32 A mgPd−1) in alkaline media. Excellent catalytic activity and long-term stability of Pd1Cu1 toward both MOR and EOR is attributed to its stable cubic morphology, composition and synergetic effect, high electrochemical active surface area (ECSA) and PdO reduction at more negative potential. In comparison to the literature, the cubic-PdCu is one of the best electorcatalyst toward MOR and EOR. The cubic-PdCu NPs as anode have potential application in direct alcohol fuel cells owing to their excellent electrochemical performance, stability and cost effectiveness.

Pt0.25Ru0.75/N‐C as Highly Active and Durable Electrocatalysts toward Alkaline Hydrogen Oxidation Reaction

AbstractA series of uniform 3.0–3.8 nm Pt1−xRux particles supported on nitrogen‐doped carbon (N‐C) is synthesized by wet‐impregnation, high‐temperature reduction, and high‐temperature NH3 etching. As far as it is known, the resultant Pt0.25Ru0.75/N‐C exhibits the highest activity toward alkaline hydrogen oxidation reaction (HOR) in terms of mass specific exchange current density (j0,m, 1654 A gPtRu−1), that is 4.7 and 1.4 times of commercial Pt/C (352 A gPt−1) and PtRu/C (1213 A gPtRu−1), respectively. The remarkable activity originates from a high electrochemical active surface area (ECSA), weakened hydrogen binding energy (HBE), and appropriate oxophilic property. Additionally, the Pt0.25Ru0.75/N‐C displays much improved durability during potential cycling with respect to commercial Pt/C and commercial PtRu/C, likely arising from the stabilizing effect of nitrogen dopant of N‐C on Pt0.25Ru0.75. Furthermore, the single cell fabricated with 0.08 mgPt cm−2 of the Pt0.25Ru0.75/N‐C as the anode reaches a peak power density of 831 mW cm−2, which is 1.8 and 1.1 times of that fabricated with 0.2 mgPt cm−2 of commercial Pt/C and 0.13 mgPt cm−2 of commercial PtRu/C as the anode, respectively. This study exhibits that low‐platinum alkaline HOR electrocatalyst should be a highly promising approach for hydroxide exchange membrane fuel cells (HEMFCs).

Atomically Dispersed Iron-Nitrogen Sites on Hierarchically Mesoporous Carbon Nanotube and Graphene Nanoribbon Networks for CO2 Reduction.

Atomically dispersed metal and nitrogen co-doped carbon (M-N/C) catalysts hold great promise for electrochemical CO2 conversion. However, there is a lack of cost-effective synthesis approaches to meet the goal of economic mass production of single-atom M-N/C with desirable carbon support architecture for efficient CO2 reduction. Herein, we report facile transformation of commercial carbon nanotube (CNT) into isolated Fe-N4 sites anchored on carbon nanotube and graphene nanoribbon (GNR) networks (Fe-N/CNT@GNR). The oxidization-induced partial unzipping of CNT results in the generation of GNR nanolayers attached to the remaining fibrous CNT frameworks, which reticulates a hierarchically mesoporous complex and thus enables a high electrochemical active surface area and smooth mass transport. The Fe residues originating from CNT growth seeds serve as Fe sources to form isolated Fe-N4 moieties located at the CNT and GNR basal plane and edges with high intrinsic capability of activating CO2 and suppressing hydrogen evolution. The Fe-N/CNT@GNR delivers a stable CO Faradaic efficiency of 96% with a partial current density of 22.6 mA cm-2 at a low overpotential of 650 mV, making it one of the most active M-N/C catalysts reported. This work presents an effective strategy to fabricate advanced atomistic catalysts and highlights the key roles of support architecture in single-atom electrocatalysis.

Ordered-Mesoporous-Carbon-Confined Pb/PbO Composites: Superior Electrocatalysts for CO2 Reduction.

CO2 electroreduction has gained significant interest. However, fabricating cost-effective nonprecious-metal electrocatalysts that can selectively convert CO2 to a specific product remains highly challenging. Herein, Pb-based materials consisting of Pb0 and PbO confined in ordered mesoporous carbon (OMC) (Pb/PbO@OMC) were constructed for CO2 electroreduction to CO. Interestingly, the activity and selectivity of the Pb/PbO@OMC varied with the molar ratio of Pb0 /PbO. The material calcined at 800 °C (Pb/PbO@OMC-800) with a Pb0 /PbO ratio of 0.58 provided the best result with CO as the only carbon-based product, and the Faradaic efficiency of CO reached 98.3 % at a high current density of 41.3 mA cm-2 . Detailed studies indicated that Pb0 , PbO, and OMC co-operated well to enhance the performance of Pb/PbO@OMC-800, which mainly originated from the good interface between Pb0 and PbO, higher electrochemical active surface area, and faster electron transfer to form the CO2 ⋅- intermediate.

Efficient hydrogen recovery with CoP-NF as cathode in microbial electrolysis cells

The emerging microbial electrolysis cell (MEC) is of great potential for energy recovery from wastewater as hydrogen, while the application of MECs required cost-effective, scalable cathodes. Here, the phosphating cobalt (CoP) acicular nanoarray in-situ growing on a 3D commercial nickel foam (NF) matrix without binder demonstrated outstanding electrocatalytic activity. The nano-CoP coated NF (CoP-NF) was assessed for hydrogen recovery performance in MEC. In electrochemical testing, the CoP-NF demonstrated comparable performance to a commercial Pt/C catalyst in linear scan voltammetry tests. The lower Tafel slope of 175.4 mV dec−1 in 1 M phosphate buffer electrolyte indicated more favorable electrochemical kinetics of CoP-NF than commercial Pt/C. The CoP-NF demonstrated higher electrochemical active surface area of electrode-liquid interface for its acicular nano-structure, while the smaller charge transfer resistance of CoP-NF suggested the faster electron transfer rate and catalytic activity of hydrogen evolution reaction. An improved hydrogen production rate of 222 ± 20.3 mL H2 L−1 d−1 at 0.7 V applied voltage in fully assembled MECs was achieved for the outstanding hydrogen evolution performance of CoP-NF cathode, which was 3-fold superior to bare NF and even better than the Pt/C. The energy efficiency based on input electricity in the MECs equipped with the CoP-NF (90 ± 6.5%) was increased to twice as much as that Pt/C based cathodes. Long-term operation tests of MECs confirmed the superior stability of CoP-NF as an effective cathode in MECs for hydrogen production, suggesting its potential possibility in practical application.

Facile Preparation of a Surface-Enriched Pt Layer Over Pd/C as an Efficient Oxygen Reduction Catalyst With Enhanced Activity and Stability

Abstract Pt-enriched surface layer formation on Vulcan carbon-supported Pd (Pt@Pd/C) was successfully prepared through a simple and one-pot formic acid reduction approach without any stabilizing agent. The electrocatalytic performance of Pt@Pd/C catalyst toward an oxygen reduction reaction (ORR) in alkaline medium was studied and also compared with standard carbon-supported Pt (Pt/C) and Pd (Pd/C) catalysts. The Pt@Pd/C exhibits higher electrochemical active surface area (74.7 m2/g) and mass activity (1.38 mA/µg) than Pt/C, Pd/C, and contending with standard reported catalysts. In durability tests, Pt@Pd/C showed negligible loss of intrinsic activity (∼10%) after 10,000 cycles which confirmed improved stability than Pt-based catalysts for ORR in KOH medium. This improved electrocatalytic performance could be attributed to their structural characteristics of the Pt-enriched surface layer on Pd/C-core and the compressive lattice strain on Pt. The present investigation demonstrates the simple preparation procedure for surface-enriched Pt on Pd/C and its improved performance for ORR, suggesting that it is a promising contender to benchmark ORR catalysts for alkaline fuel cells.

On a Two-Dimensional MoS2/Mo2CTx Hydrogen Evolution Catalyst Obtained by the Topotactic Sulfurization of Mo2CTx MXene

Herein we topotactically reacted sulphur, S, with Mo2CTx MXene powders to synthesize Mo2CTx sheets covered by MoS2 nanosheets and tested the resulting material as a hydrogen evolution reaction, HER, electrocatalyst. As a result, a high electrochemical active surface area catalyst was obtained. It allows driving a current density of 10 mA cm−2 at a low overpotential of only 150 mV. Stabilization of the water activated complex as well as interfacial charge transfer accompanied by changes in the adsorption energy hydrogen are most likely responsible for the high electrochemical activity. Moreover, no efficiency loss was observed under working conditions during 30 h in a 1 mol l−1 KOH electrolyte, confirming the remarkable electrochemical stability of this composite catalyst.

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo2C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo2C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo2C (Mo2C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo2C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec−1) and overpotential of 186.6 mV to drive current density of 10 mAcm−2. It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.

Hollow Nanotube Ru/Cu2+1 O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting.

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu2+1 O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu2+1 O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu2+1 O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm-2 in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm-2 in the OER. Importantly, the alkaline electrolyzer using Ru/Cu2+1 O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm-2 , which is much lower than the benchmark of IrO2 (+)/Pt(-) counterpart (1.64 V at 10 mA cm-2 ). The excellent performance of the Ru/Cu2+1 O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.

Optimizing metal-support interphase for efficient fuel cell oxygen reduction reaction catalyst

The development of cost-effective and highly-efficient electro-catalysts is essential for the advancement of proton exchange membrane fuel cells (PEMFC). We present a novel nitrogen-sulphur co-doped carbon nanotubes-few layer graphene1D-2D hybrid support formed by partially exfoliating multiwall carbon nanotubes (PECNT), to improve interface bonding to catalyst nanoparticles. Detailed Raman spectroscopy and STEM-EDS analyses demonstrate that active sites on the co-doped hybrid support ensure both uniform distribution and improved bonding of the catalyst nanoparticles to the support. Electrochemical studies show that Pt nanoparticles decorated on nitrogen-sulphur co-doped PECNT (Pt/NS-PECNT) have higher electrochemical active surface area and mass activity accompanied by low H2O2 formation and improved positive half-wave potential, as compared to those decorated on co-doped rGO-incorporated PECNT hybrid structure (Pt/NS-(rGO-PECNT)). Fuel cell measurements demonstrate a higher power density for our novel (Pt/NS-PECNT) electro-catalyst when compared to both Pt/NS-(rGO + PECNT), and commercial Pt/C electro-catalyst. We demonstrate in this work that the interconnectivity between Pt-nanoparticles and the dopant or defect sites on the support play a crucial role in enhancing the ORR activity, fuel cell performance, and durability of the catalyst.

A Lactate/Oxygen Biofuel Cell: The Coupled Lactate Oxidase Anode and PGM-Free Fe-N-C Cathode.

The rapid development of both wearable and implantable biofuel cells has triggered more and more attention on the lactate biofuel cell. The novel lactate/oxygen biofuel cell (L/O-BFC) with the direct electron transfer (DET)-type lactate oxidase (LOx) anode and the platinum group metal (PGM)-free Fe-N-C cathode is designed and constructed in this paper. In such a reasonable design, the surface-controlled direct two-electron electrochemical reaction of the lactate oxidase was determined by cyclic voltammetry (CV) on the carbon nanotube (CNT) modified electrode with favorable high electrochemical active surface area and electronic conductivity. Additionally, the biosensor based on DET-type LOx modified electrode impressively presented linear response to lactate with different concentrations from 0.000 mM to 12.300 mM. In particular, the apparent Michealis-constant (KMapp) calculated as 0.140 mM clearly indicates that LOx on CNT has strong affinity to the substrate lactate. Meanwhile, 4e- transfer oxygen reduction reaction (ORR) was proven to take place on the Fe-N-C catalysts inthe 0.1 M PBS system, indicating the advantage by using the Fe-N-C catalysts at the cathode of L/O-BFC. Last but not least, the L/O-BFC with the direct electron transfer (DET)-type lactate oxidase(LOx) anode and the Fe-N-C cathode produced an superior open circuit potential (OCP) of 0.264 V and a maximum output power density (OPD) of 24.430 μW cm-2 in O2 saturated 95.020 mM lactate solution. The above results will not only bring about significant interest in developing a DET-type biofuel cell, but also offer guiding direction to explore novel catalyst materials for the biofuel cell. This work enriches the research content and may push developments of the implantable and wearable biofuel cell forward.

Electrostatic spraying of membrane electrode for proton exchange membrane fuel cell

In order to improve the performance of proton exchange membrane fuel cell (PEMFC), the optimization of electrostatic spraying of membrane electrode was conducted. The influence of the spraying voltage on morphology, elemental composition of catalyst layer, and performance of the PEMFC were investigated. The results show that increasing spraying voltage could reduce agglomeration of the carbon-supported platinum particles, leading to more uniform pore distribution. High voltage did not accelerate oxidation of platinum catalyst. A high electrochemical active surface area of 26.18 m2/gpt was obtained when the platinum-carbon catalyst layer was deposited in cone jet mode. With further increasing spraying voltage, the total ohmic resistance and catalytic activity were changed slightly, whereas the charge transfer resistance was increased. Using the optimized electrostatic spraying parameters (injection rate = 100 μL min−1, spraying voltage = 8.5 kV, and working distance = 12 mm), a peak power density of 1.408 W cm−2 was obtained with an output voltage of 0.451 V.

Uniform and Size‐Controlled Synthesis of Pt Nanoparticle Catalyst by Fluidized Bed Reactor Atomic Layer Deposition for PEMFCs

AbstractPt nanoparticles (NPs) on a carbon support (Pt/C) are deposited by a simple fluidized bed reactor atomic layer deposition (FBR‐ALD) technique. The growth characteristics of the Pt NPs are investigated as a function of ALD cycles from 5 to 30 cycles. The excellent characteristics of FBR‐ALD offer highly dispersed and dense Pt particles with a size of ≈1 nm at low ALD cycles (5 cycles). However, as the number of ALD cycles increases above 5, the NPs increase in size and agglomerate due to preferential growth of incoming Pt NPs on previously deposited Pt surfaces. An electrochemical study shows that low ALD cycles (5 cycles) for the Pt/C catalyst result in a high electrochemical active surface area (ECSA) (114.67 m2 g−1). With increasing the number of cycles, ECSA is found to decrease, but still apparently higher than that of commercial Pt catalyst with the similar Pt wt% loading. Finally, ALD Pt/C catalysts with various cycles are applied to fuel cell testing for power generation. The electrode prepared with 20 ALD cycles of the Pt/C catalyst shows the best fuel cell performance (1.58 A cm−2 at 0.6 V) due to an adequate combination of activity and mass transfer characteristics of the electrode.

Self-Destruction of Cancer Induced by Ag2 S Amorphous Nanodots.

Studies on distinctive performances and novel applications of amorphous inorganic nanomaterials are becoming attractive. Herein, Ag2 S amorphous and crystalline nanodots (ANDs and CNDs) are prepared via facile methods. In vitro and in vivo studies indicate that Ag2 S ANDs, rather than CNDs, can induce the self-destruction of tumors, which can be attributed to their distinctive chemical properties, e.g., the higher electrochemical active surface area and lower redox potential well matching with the redox reaction requirement in the tumor microenvironment. Ag2 S ANDs can be oxidized by intracellular reactive oxygen species (ROS) to release Ag+ , which further stimulates high generation of intracellular ROS. This mutual stimulation damages the mitochondria, induces apoptosis, and leads to the self-destruction of the tumor. Moreover, Ag2 S ANDs do not show observable in vitro and in vivo side effects. These findings provide a promising self-destructive strategy for cancer therapy by utilizing distinctive chemical properties of inorganic nanomaterials, while avoiding complicated external assistance.

Controlled synthesis of tubular ferrite MFe2O4 (M = Fe, Co, Ni) microstructures with efficiently electrocatalytic activity for water splitting

Ferrite MFe2O4 (M = Fe, Co, Ni) tubular microstructures were successfully synthesized through a simple two-step strategy. The tubular FeOOH microstructures were first obtained by a heating reflux route. Then, tubular ferrite MFe2O4 (M = Fe, Co, Ni) microstructures were produced by a solvothermal method. The as-prepared products were characterized by the powder X-ray diffraction (XRD), the field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and EDS mapping. Experiments showed that as-obtained ferrite catalysts demanded the overpotentials of −201∼-359 mV or ∼340–432 mV to afford the current density of −/+10 mA cm−2 for hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) with long-term durability for 50 h in 1.0 M KOH solution. Among them, NiFe2O4 tubular microstructures presented the best electrocatalytic activities for HER and OER due to the largest BET specific surface area, the highest electrochemical active surface area and the smallest charge-transfer resistance. Obviously, the present ferrite tubular microstructures have potential application as a bifunctional electrocatalyst for full water splitting.

Zinc Cobalt Sulfides on N, S Co-Doped Carbon Derived from Bimetallic-Organic Framework As an Advanced Electrocatalyst for Oxygen Reduction Reaction

Recently, the environmental problems caused by excess use of fossil fuels triggered intense research for efficient, inexpensive, and harmless energy conversion and storage devices such as fuel cells and rechargeable metal air batteries. In these applications, the oxygen reduction reaction (ORR) are a key electrochemical process for commercialization. Also, developing non-noble metal-based electrocatalysts with high electrochemical performance is very important in economic point of view. To address these issues, electrocatalysts based on nanocarbon frameworks such as metal organic frameworks (MOFs) and zeolitic imidazolate framework (ZIF) have been widely investigated as promising alternatives to Pt-based catalysts. In this work, we prepared bi-metallic ZIFs by coprecipitation of zinc and cobalt ions in the presence of 2-methylimidazole, followed by one-step sulfidation and carbonization to synthesize zinc cobalt sulfides supported on N, S co-doped porous carbon. The as-synthesized catalyst maintained inherent dodecahedral particle shape of ZIF. Furthermore, it exhibits outstanding ORR onset-potential (0.96 V vs. RHE) and half-wave potential (0.83 V vs. RHE), which is comparable to commercial Pt/C catalyst in alkaline electrolyte. Such outstanding electrochemical properties are mainly ascribed to the synergistic effect of the chemical composition, high electrochemical active surface area, and abundant active sites of the dodecahedral structure. These findings suggest that the transition metal sulfides on N, S co-doped porous carbon can be a promising alternative for the next generation of energy storage and conversion technologies.

Preparation of Pt dendrites on Poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide as an enhanced electrocatalyst for the hydrogen evolution reaction in alkaline media

Herein, we describe the synthesis of Pt dendrites with electrochemically active high-index planes on poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (PFG) using a newly developed high-voltage electrochemical reduction (HVER) method. Subsequently, the catalytic activities of the prepared samples for the hydrogen evolution reaction (HER) in 1 M NaOH are characterized. The HVER method facilitates the preparation of nanoparticles in short reaction times. This method allows Pt particles to be formed by electron transfer from the cathode to a Pt precursor. Importantly, Pt particles deposited on PFG (Pt/PFG), prepared by the addition of PVP, are revealed to comprise both two- (2D) and three-dimensional (3D) dendrite structures, featuring abundant step and edge sites. The various factors affecting the morphology and the ratio of 2D to 3D dendrites of Pt were determined by TEM analysis. The ratio of 2D to 3D Pt dendrites depends on the amount of PVP employed and has a direct influence on the electrochemically active surface area (ECSA) and HER activity. Namely, the prepared Pt/PFG sample with the highest density of 2D Pt dendrites exhibits the highest HER activity due to its high ECSA. The performance of Pt/PFG13 (prepared keeping the PVP:Pt ratio as 13:1) was compared with that of commercial 40 wt% Pt/C, and the Pt/PFG13 sample exhibited superior current density (−424 mA/cmgeo2 for Pt/PFG13 and –242 mA/cmgeo2 for commercial 40 wt% Pt/C at −1.5 V vs. Hg/HgO; approximately 1.8 times higher) and catalytic stability, implying that these parameters are positively correlated with the increased number of step and edge sites.

Asphaltene-Derived Metal-Free Carbons for Electrocatalytic Hydrogen Evolution.

The design of new and improved catalysts is an exciting field and is being constantly improved for the development of economically, highly efficient material and for the possible replacement of platinum (Pt)-based catalysts. In this, carbon-based materials play a pivotal role due to their easy availability and environment friendliness. Herein, we report a simple technique to synthesize layered, nitrogen-doped, porous carbon and activated carbons from an abundant petroleum asphaltene. The derived nitrogen-doped carbons were found to possess a graphene-like nanosheet (N-GNS) texture with a significant percentage of nitrogen embedded into the porous carbon skeleton. On the other hand, the activated porous carbon displayed a surface area (SA) of 2824 m2/g, which is significantly higher when compared to the nitrogen-doped carbons (SA of ∼243 m2/g). However, the nonactivated N-GNS were considered as an attractive candidate due to their high electrochemical active surface area, the presence of a mixture of porous structures, uniform layers, and effective doping of nitrogen atoms within the carbon matrix. Importantly, the hydrogen evolution reaction activity of the derived N-GNS sample illustrates a significant catalytic performance when compared to that of other nonfunctionalized carbons. Our current finding demonstrates the possibility of converting the asphaltene wastes into a high-value-functionalized porous carbon for catalytic applications.

Bioelectrochemical deposition of palladium nanoparticles as catalysts by Shewanella oneidensis MR-1 towards enhanced hydrogen production in microbial electrolysis cells

Catalysts are critically important to accomplish hydrogen evolution reaction in microbial electrolysis cells (MECs). Herein, palladium nanoparticles were generated directly on a cathode electrode by bioelectrochemical reduction with Shewanella oneidensis MR-1 and then applied to produce hydrogen gas in MECs. The MEC with bioelectrochemically deposited Pd catalysts achieved a hydrogen production rate of 61.8 ± 2.0 L-H2 m−3 d−1, significantly higher than 38.5 ± 2.0 L-H2 m−3 d−1 with the Pd catalysts in the absence of microbial reduction. This improvement was related to a higher electrochemical active surface area of 40.5 ± 3.5 m2 g−1 and smaller Pd particle size (10–100 nm) on the cathode with bioelectrochemical deposition, compared to those of electrochemically-generated Pd catalysts (16.8 ± 2.8 m2 g−1 and 200–250 nm, respectively). The superior performance of the bioelectrochemically deposited Pd catalysts was supported by a much smaller charge transfer resistance of 15.4 Ω. Although microorganisms could help generate better Pd catalysts, the lack of strong bond between Pd nanoparticles and carbon cloth resulted in unstable hydrogen production performance. Applying a binding agent – Nafion led to consistent current generation and hydrogen production. The results of this study encourage further exploration of in situ deposition of catalysts via bioelectrochemical reactions for MEC applications.