Electrocatalytic hydrogen production on GCE/RGO/Au hybrid electrode

We have prepared a nanocomposite hybrid film to produce a collaborative network of gold (Au) nanoparticles that are highly dispersed on reduced graphene oxide (RGO) sheets, and tested it for electrocatalytic hydrogen production. The RGO/Au nanocomposite film synthesized on glassy carbon electrode (GCE) allows significant improvements to the electron-transfer process. The Au nanoparticles decorated on the surface of graphene increases the electron density, which synergistically promote the adsorption of hydrogen atoms on the graphene sheets and consequently enhance the hydrogen evolution reaction (HER) activity. The surface properties of the composite was characterized by field-emission scanning electron microscopy (FE-SEM) and the electrocatalytical performances evaluated as-prepared electrocatalyst toward (HER) by linear sweep voltammetry (LSV), Tafel polarization curves and electrochemical impedance spectroscopy (EIS) analyses. The GCE/RGO/Au nanohybrid electrode exhibited good catalytic activity for HER with an onset potential of ?0.3 V and a Tafel slope of 136 mV dec^?1, achieving a current density of 10 mA cm^?2 at an overpotential of ?0.43 V.     

Ultrafine Co6Mo6C nanocrystals on reduced graphene oxide as efficient and highly stable electrocatalyst for hydrogen generation

Up to now, it is still a great challenge to develop active, durable and low-cost non-precious metal catalysts toward hydrogen evolution reaction (HER). In this paper, we synthesized ultrafine Co₆Mo₆C nanocrystals on reduced graphene oxide (RGO) support (Co₆Mo₆C/RGO). The Co₆Mo₆C/RGO shows Pt-like HER performance, which exhibits almost zero onset overpotential, and very small overpotential of 64 mV at 10 mA cm^?2. In addition, the Co₆Mo₆C/RGO has a very small Tafel slope of 44 mV dec^?1 and a high exchange current density of 0.402 mA cm^?2, suggesting fast reaction kinetics. Furthermore, the Co₆Mo₆C/RGO demonstrates superior durability in acid electrolyte. The distinguished HER performance makes Co₆Mo₆C/RGO the promising candidate as non-precious metal catalyst for HER in acid electrolyte.     

Noble metal-free cuprous oxide/reduced graphene oxide for enhanced photocatalytic hydrogen evolution from water reduction

Cu₂O loaded reduced graphene oxide (Cu₂O/RGO) was prepared via a one-step in-situ reduction method. Composition and structure of the Cu₂O/RGO were characterized by X-ray diffraction, high resolution transmission electron microscope and X-ray photoelectron spectroscopy. With eosin Y (EY) and rose bengal (RB) as co-sensitizers, the activity of hydrogen evolution over the Cu₂O/RGO dramatically increased and achieved a maximum when the loading amount of Cu on the RGO was about 3 wt.%. It exceeded that of RGO and Cu₂O by a factor of 7.3 and 4.2 at the same conditions, respectively. It could be even comparable to that of the Pt/RGO under the same reaction conditions. This work showed a possibility of utilizing Cu₂O as an alternative for noble metals (such as Pt) due to its low cost and high performance in photocatalytic hydrogen production.     

Effect of alkaline-doping on photoelectrochemical activity of electrodeposited cuprous oxide films

P-type Cu₂O films with alkaline ions (Li⁺, Na⁺ and K⁺) of unintentional dopants on indium tin oxide coated glass substrate are successfully fabricated via a simple electrodeposition method for photoelectrochemical (PEC) hydrogen generation. The SEM and XRD analysis show the as-grown films with the pyramid-like morphology and cubic structure, and the composition of alkaline-doped Cu₂O films are examined using XPS spectroscopy to demonstrate the substitution of alkaline ions in the Cu₂O lattice. The optical analyses, including the absorbance and low-temperature photoluminescence spectra, confirm a bandgap of 2.3 eV and the presence of structural defects in alkaline-doped Cu₂O films. The Mott-Schottky plot shows the flat band potentials of the alkaline-doped Cu₂O films to be approximately ?0.1 V and the hole concentrations in the order of 10¹⁷ cm^?3. Significantly, the Cu₂O:Li film photocathode exhibits a higher photocurrent of ?2.2 mA cm^?2 at a potential of ?0.6 V vs Ag/AgCl which are greater than those of Cu₂O:K and Cu₂O:Na films due to greater preferred orientation degrees along (111) and less structural defects, because the ionic radii of Cu and Li is similar. These results demonstrate the great potential of alkaline doped Cu₂O films in solar-related applications.     

Facile synthesis of well dispersed Pd nanoparticles on reduced graphene oxide for electrocatalytic oxidation of formic acid

In present study, we report a facile synthesis of crystalline, small size Pd nanoparticles (NPs) on reduced graphene oxide (RGO) abbreviated as Pd/RGO for electrocatalytic oxidation of formic acid (FA). Here, first graphene oxide (GO) was reduced by the green method using l-ascorbic acid and citric acid and further Pd NPs were decorated on RGO by a facile method without using any reducing agents. The reduction of GO to RGO and synthesis of Pd NPs was confirmed by the X-ray diffraction (XRD) and X-ray photoelectrons (XPS) techniques. Surface morphology of Pd/RGO nanocomposite was evaluated by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The electrocatalytic behavior of Pd/RGO nanocomposite was tested by using of cyclic voltammetric (CV) technique for electro-oxidation of FA in mixed solution of 0.5 M HCOOH + 0.5 H₂SO₄ at RT. Results shows that the higher electrocatalytic activity of Pd/RGO nanocomposite compare to Pd NPs.     

Surface modification of aligned TiO2 nanotubes by Cu2O nanoparticles and their enhanced photo electrochemical properties and hydrogen generation application

In this work, we report the synthesis of cuprous oxide (Cu₂O) nanoparticles modified vertically oriented aligned titanium dioxide (TiO₂) nanotube arrays through wet chemical treatment of TiO₂ nanotubes and their multi-functional application as enhanced photo electrochemical and hydrogen generation. The synthesized samples were characterized by X-ray diffraction, SEM, TEM, and UV–Vis spectroscopy. The structural characterization revealed that the admixed Cu₂O nanoparticles on the TiO₂ surface did not alter its crystalline structure of vertically oriented aligned TiO₂ nanotube. The photocatalytic performance and hydrogen generation of as synthesized Cu₂O nanoparticles modified aligned TiO₂ nanotube was found to highly depend on the Cu₂O content. The optical characterizations reveal that the presence of Cu₂O nanoparticles extends its absorption into the visible region which improves the photocurrent density in comparison to pristine aligned TiO₂ nanotubes electrodes due to enhanced photoactivity and better charge separation. The optimum photocurrent density and hydrogen generation rate has been found to be 3.4 mA cm^?2 and 127.5 μmole cm^?2 h^?1 in 1 M Na₂SO₄ electrolyte solution under 1.5 AM solar irradiance of white light with illumination intensity of 100 mW cm^?2.     

Nanoscale engineering MoP/Fe2P/RGO toward efficient electrocatalyst for hydrogen evolution reaction

The preparation of hydrogen evolution reaction (HER) electrocatalyst with high catalytic performance is a huge challenge. In this work, we develop a MoP/Fe₂P/RGO composite as a electrocatalyst for HER. The MoP/Fe₂P/RGO exhibits excellent electrocatalytic performance with a Tafel slope and an onset overpotential of 51 mV/dec and 105 mV, respectively. To drive 10 mA/cm², it only requires a small over-potential of 156 mV. The high electrocatalytic HER activity is mainly due to the synergistic effect of MoP and Fe₂P. In addition, the introduction of RGO not only prevents particle aggregation and coalescence during high temperature phosphating, but also improves the conductivity of the catalyst.     

Fabrication of cost-effective non-noble metal supported on conducting polymer composite such as copper/polypyrrole graphene oxide (Cu2O/PPy–GO) as an anode catalyst for methanol oxidation in DMFC

Cost-effective non-noble metal catalysts are of key significance to the successful use of direct methanol fuel cells (DMFCs) for electricity generation. Herein, cuprous oxide nanoparticles (Cu₂O NPs) supported graphene oxide (GO), polypyrrole (PPy) and polypyrrole–graphene oxide (PPy–GO) matrices were prepared using borohydride reduction method. The prepared catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectra, Zeta potential and transmission electron microscopy (TEM). The elemental analysis of the composites was done by energy dispersive X-ray spectroscopy (EDX). Cu₂O NPs were homogeneously dispersed and strongly anchored on the PPy grafted GO matrix and this was examined through morphological analysis. The Cu₂O/PPy–GO (80:10:10) NPs exhibited noticeable improvement in electrochemical performance in comparison to pure graphene oxide (GO) and pure PPy supported Cu₂O NPs catalyst and revealed the peak current density of 300 μA cm^?2 at +0.68 V. The Cu₂O/PPy–GO system demonstrated higher current density and also exhibited greater stability in comparison to the commercial Pt–Ru/C catalyst as characterized by chronoamperometry (CA) analysis. This prospective nano-catalyst showed higher I_F/I_B ratio (26%, 8.6% and 19%) compared to the corresponding catalyst systems of Cu₂O/GO, Cu₂O/PPy and Pt–Ru/C. In direct methanol fuel cell (DMFC), the efficiency of Cu₂O/PPy–GO nano-catalyst system as an anode catalyst for methanol oxidation reaction (MOR) was investigated and the result revealed a maximum current density of 155 mA cm^?2 at +0.2 V and power density of 31 mW cm^?2. Hence, Cu₂O/PPy–GO NPs are a cost-effective alternative for Pt–Ru/C system to execute practical application in DMFC.     

Preparation of porous polyaniline/RGO composite and its application in improving the electrochemical properties of Co9S8 hydrogen storage alloy

The sea urchin-like porous polyaniline (PPANI) is prepared by a facile saturated solution synthetic route. The porous polyaniline/reduced graphene oxide composite (PPANI/RGO) is synthesized via a solution-assisted self-assembly method. Mechanical alloying is used to obtain the Co₉S₈ alloy. Composites of Co₉S₈ mixed with PPANI and PPANI/RGO are fabricated through ball-milling to improve the electrochemical performance of Co₉S₈ alloy. The structures and morphologies of the composite alloys are studied by XRD, SEM and BET. The electrochemical properties of alloys are tested as negative electrodes of Ni-MH batteries by the LAND CT2001A tester and three-electrode system. For comparison, Co₉S₈ alloys doped with conventional polyaniline (CPANI) and RGO are also prepared. Ultimately, the Co₉S₈ + PPANI composite shows preferable discharge capacity compared with CPANI modified Co₉S₈ and matrix alloy. In addition, the PPANI/RGO composite modified Co₉S₈ electrode exhibits superior discharge capacity than separate PPANI and RGO coated alloys. A maximum discharge capacity (701.4 mAh/g) is achieved for Co₉S₈ + PPANI/RGO electrode. Furthermore, the Co₉S₈ + PPANI/RGO composite materials exhibit preferable high-rate dischargeability, improved corrosion and oxidation resistance and excellent kinetics properties. The PPANI material with special porous structure and unique morphology displays better performance than CPANI. Moreover, a synergistic effect between PPANI and RGO species in the PPANI/RGO material may provide a rapid passageway for charge transfer and accelerate the hydrogen transmission. Accordingly, the electrochemical activity and kinetic properties are improved for Co₉S₈ + PPANI/RGO composite electrode.     

Nitrogen and nitrogen-sulfur doped graphene nanosheets for efficient hydrogen productions for HER studies

Carbon based electrocatalysts are promising candidates to achieve the production of hydrogen energy in a sustainable wayby simple water splitting technique. Thermally treated reduced graphene oxide (RGO) and N–S doped RGO employing urea and thiourea as electrocatalysts for hydrogen evolution reaction (HER). The performance of electrochemical HER has been thoroughly examined via linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. Furthermore, the Raman I_D/I_G ratio of RGO, N-RGO and NS-RGO were found to be 1.43, 1.10 and 1.11 respectively. From electrochemical HER analysis, we found that the NS-doped RGO exposed the low overpotential, low Tafel slope and low solution resistance value of 211 mV, 197 mV/dec and 0.34 Ω respectively. In addition, the chronoamperometry study revealed, the electrocatalyst NS-RGO showed an excellent stability (81.3% retention) with low 211 mV and remained unchanged for more than 16 h. Therefore, this work concludes that heteroatom dopant participate in improving electrocatalytic HER action.     

Surfactant-free Pd–Fe nanoparticles supported on reduced graphene oxide as nanocatalyst for formic acid oxidation

Herein, a novel surfactant-free nanocatalyst of Pd–Fe bimetallic nanoparticles (NPs) supported on the reduced graphene oxide (Pd–Fe/RGO) were synthesized using a two-step reduction in aqueous phase. Electrochemical studies demonstrate that the nanocatalyst exhibits superior catalytic activity towards the formic acid oxidation with high stability due to the synergic effect of Pd–Fe and RGO. The optimized Pd–Fe/RGO (Pd:Fe = 1:5) nanocatalyst possess an specific activity of 2.72 mA cm^?2 and an mass activity of 1.0 A mg^?1_(Pd), which are significantly higher than those of Pd/RGO and commercial Pd/C catalysts.     

The effect of oxygen–containing functional groups on the H2 adsorption of graphene–based nanomaterials: experiment and theory

The oxygen–containing functional groups of graphene oxide (GO) play an important role in hydrogen storage. In addition to the contribution of the specific surface area and micro–porous porosity, the interactions of the functional groups with H₂ molecules are also an important factor in the aspect of GO hydrogen storage. This paper explores the oxygen–containing functional groups affecting the hydrogen physisorption capacity of the GO and reduced graphene oxide (RGO) by experimental H₂ adsorption measurement and theoretical calculation. Experimental results related to synthesis of GO and RGO via the modified Hummer's method and characterized using SEM, TEM, SAED, XRD, FTIR, TGA and Raman spectroscopy, are presented. Compared with RGO, the surface and edge of GO contain a large amount of oxygen–containing functional groups and its specific surface area is slightly increased through BET measurement. GO is found to exhibit better H₂ uptake capacity (0.74 wt%) as compared to RGO (0.47 wt%) at 77 K and pressure up to 10 bars. The density functional theory is applied to optimize the adsorption configurations of H₂ on the surface of samples. Calculation results show that the adsorption on the GO can be promoted by surface functional groups epoxy, hydroxyl, carboxyl and carbonyl; the enhancement of hydroxyl is greater than other species on the surface and the maximal adsorption energy reaches to ?0.112 eV which is about twice that of graphene. As indicated above, these functional groups could be formed easily on the graphene surface, which not only enhance specific surface area and interlayer spacing, but also significantly change the location of carbons, redistributing the electron structure of graphene and enhancing the adsorption energy.     

Mechanistic investigation on tuning the conductivity type of cuprous oxide (Cu2O) thin films via deposition potential

The conductivity type of cuprous oxide (Cu₂O) thin films is tuned by controlling the deposition potential of an electrochemical process in an acid cupric acetate solution containing sodium dodecyl sulfate. The morphology and chemical composition of the deposited Cu₂O films are studied by SEM, XRD and XPS. The change of the conductivity type of Cu₂O films is further studied through zero-bias photocurrent and Mott-Schottky measurements. The results indicate that the Cu₂O films behave as n-type semiconductors when the overpotentials are low (potentials higher than ?0.05 V) and p-type semiconductors when the overpotentials are high (potentials lower than ?0.10 V). The transformation of conductivity from n-type to p-type comes from the competition reactions between forming Cu₂O and forming metallic Cu from Cu²⁺. When the potential is lower than ?0.10 V, most of Cu²⁺ are consumed by the growth of metallic Cu at the film/solution interface, so that the Cu²⁺ provided to grow Cu₂O film are insufficient and copper vacancies form in the film, leading to the p-type conductivity.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

Efficient hydrogen evolution catalytic activity of graphene/metallic MoS2 nanosheet heterostructures synthesized by a one-step hydrothermal process

Metallic (1T)-transition metal dichalcogenides is of excellent optical and electrical properties and so especially suitable for various applications including hydrogen evolution catalysis, electronics, and photoelectrons. To date, achieving 1T-MoS₂ nanosheets with a simple chemical process still is a challenge. Here we report a hydrothermal synthesis of the 1T-MoS₂ nanosheets by incorporating reduced graphene oxide (RGO) or using citric acid/slow successive heating. A small amount of RGO induced the formation of pure 1T-MoS₂ nanosheets. Citric acid/slow successive heating induced the formation of 1T-MoS₂ nanosheets with a small amount of 2HMoS₂. Citric acid/slow successive heating also resulted in smaller average particle size in the present of RGO. Synthesized 1T-MoS₂ nanosheets and RGO/1T-MoS₂ nanosheet hybrids showed remarkably enhanced conduction and wettability compared with their semiconductor (2H)-nanostructures. Thus, dramatically enhanced hydrogen evolution catalytic activity and stability compared with the 2H-nanostructures were observed. RGO/1T-MoS₂ nanosheet hybrids synthesized by incorporating graphene oxide and using citric acid/slow successive heating exhibited greatest photocatalytic activity (71.2 mmol./g·h) and electrocatalytic activity (onset potential of ?15 mV vs. reversible hydrogen electrode and Tafel slopes of 43 mV/decade). These facile processes might also be significant for the synthesis and application of other 1T-transition metal dichalcogenides nanosheets and their hybrids with RGO.     

Computational studies of electrochemical CO2 reduction on chalcogen doped Cu4 cluster

By use of the theoretical method of density functional theory (DFT), we systemically investigate the chalcogen doped Cu₄ metal clusters (Cu₄O, Cu₄S, and Cu₄Se) as catalysts for the electrochemical CO₂ reduction with toluene as solvent. These doped clusters have efficient catalytic properties which can reduce CO₂ to CH₄ and a small amount of CH₃OH. In the case of CO₂ hydrogenation to CH₄, the reaction barrier of the Cu₄O cluster and Cu₄S cluster are reduced by 0.37 eV and 0.15 eV, respectively, compared with the pristine Cu₄ cluster. The calculation results also show the overpotentials for the CO₂ hydrogenation to CH₄ in the order of Cu₄S < Cu₄O < Cu₄Se. In?addition, the geometry structures, the electronic properties, and the reaction free energies on the chalcogen doped Cu₄ clusters are also discussed to further reveal the reaction mechanism in the CO₂ electroreduction process. We hope that our present work will enlighten extensive studies on the modified electrode to decrease the limiting potential and provide a reference for the subsequent studies.     

Preparation of TiO2 nanofibers,porous nanotubes,RGO/TiO2 composite by electrospinning and hydrothermal synthesis and their applications in improving the electrochemical hydrogen storage properties of Co2B material

Co₂B hydrogen storage material was prepared via a high temperature solid phase process. The TiO₂ nanofibers (TiO₂–NF) and TiO₂ porous nanotubes (TiO₂-NT) with different size, structure and morphology were fabricated by electrospinning and hydrothermal synthesis. In order to improve the conductivity, the reduced graphene oxide/TiO₂ nanotubes composite (RGO/TiO₂-NT) was synthesized by an alkaline hydrothermal process. The three-dimensional porous TiO₂ nanotubes were attached to the two-dimensional RGO and formed a uniform dispersion. For the purpose of improving the electrochemical performance of Co₂B, composites of Co₂B doped with TiO₂–NF, TiO₂-NT and RGO/TiO₂-NT were manufactured by ball milling. Ultimately, all the composite electrodes showed higher discharge capacities than ordinary Co₂B. Among them, Co₂B modified with RGO/TiO₂-NT exhibited the highest discharge capacity (691.4 mAh/g). TiO₂-NT with large specific surface area and unique tubular porous structure can offer sufficient electrochemical active sites to anchor hydrogen and improve the electrocatalytic activity of Co₂B, meanwhile, the RGO component in RGO/TiO₂-NT with excellent electrical conduction can further provide fast channels for charger transfer during the charging/discharging processes. Moreover, the corrosion resistance, HRD and kinetics performance of Co₂B were also enhanced after doping of TiO₂–NF, TiO₂-NT and RGO/TiO₂-NT.     

Hydrothermal synthesis of mixed crystal phases TiO2–reduced graphene oxide nanocomposites with small particle size for lithium ion batteries

A rutile and anatase mixed crystal phase of nano-rod TiO₂ and TiO₂–reduced graphene oxide (TiO₂–RGO) nanocomposites with small particle size were prepared via a facile hydrothermal approach with titanium tetrabutoxide and graphene oxide as the precursor. Hydrolysis of titanium tetrabutoxide and mild reduction of graphene oxide were simultaneously carried out. Compared with traditional multistep methods, a novel green synthetic route to produce TiO₂–RGO without toxic solvents or reducing agents was employed. TiO₂–RGO as anode of lithium ion batteries was characterized by extensive measurements. The nanocomposites exhibited notable improvement in lithium ion insertion/extraction behavior compared with TiO₂, indicating an initial irreversible capacity and a reversible capacity of 295.4 and 112.3 mA h g⁻¹ for TiO₂–RGO after 100 cycles at a high charge rate of 10 C. The enhanced electrochemical performance is attributed to increased conductivity in presence of reduced graphene oxide in TiO₂–RGO, a rutile and anatase mixed crystal phase of nano-rod TiO₂/GNS composites, small size of TiO₂ particles in nanocomposites, and enlarged electrode–electrolyte contact area, leading to more electroactive sites in TiO₂–RGO.     

Investigation on energy storage and conversion properties of multifunctional PANI-MWCNT composite

Polyaniline-multiwalled carbon nanotube (PANI-MWCNT) composite synthesized through chemical polymerization is investigated as a possible electrode material for supercapacitor as well as an electro-catalyst for hydrogen evolution reaction (HER) in acidic medium. UV–Vis spectroscopy, FTIR spectroscopy and field emission scanning electron microscopy (FESEM) have been used to characterize the electrode material. The binder-free electrodes were prepared and they exhibit a specific capacitance of 540.29 F g^?1 at a scan rate of 2 mV s^?1 in 1 M H₂SO₄ electrolyte. The material exhibits excellent pseudocapacitive behaviour due to the presence of PANI with long-term cyclic stability of 87.4% retention after 5000 cycles. PANI-MWCNT composite also shows good HER activity, with overpotential of ?395 mV.