Pt-free Electrocatalysts Research Articles

Heterogeneous Ir3Sn–CeO2/C as alternative Pt-free electrocatalysts for ethanol oxidation in acidic media

For reducing the Pt usage and driving down the cost of fuel cells, it is urgent to develop alternative Pt-free catalysts with high catalytic performance. In this study, an Ir3Sn–CeO2/C heterogeneous catalyst is designed as low-price, alternative Pt-free electrocatalyst towards ethanol oxidation reaction (EOR) in acidic conditions. Owing to the strong synergistic effect among Ir, Sn and CeO2 components, Ir3Sn–CeO2/C heterogeneous catalyst exhibits higher catalytic activity and stability for EOR in comparison with commercial Pt/C, as-prepared Ir/C and Ir3Sn/C. Additionally, kinetics and mechanisms of EOR are also investigated. It proves that ethanol electrooxidation on Ir3Sn–CeO2/C catalyst is a diffusion controlled irreversible process. Meanwhile, the H2SO4 and ethanol concentrations can affect the EOR activity. All results demonstrate Ir3Sn–CeO2/C heterogeneous catalyst is a promising Pt-free choice for EOR.

Oxygenophilic ionic liquids promote the oxygen reduction reaction in Pt-free carbon electrocatalysts

We propose a novel idea to improve the surface properties of carbon-based Pt-free electrocatalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and Alkaline Fuel Cells (AFCs).

Bismuth-based ternary nanowires as efficient electrocatalysts for dye sensitized solar cells.

Bismuth-based ternary nanowires (NWs), including Bi19S27Br3 and Bi19S27I3, have been exploited as cost-effective and highly efficient Pt-free electrocatalysts in dye sensitized solar cells (DSSCs). Devices with them as counter electrodes (CEs) display a power conversion efficiency (PCE) of over 8.70%, superior to that of a cell with Pt as a CE (7.99% PCE) under the same conditions.

Correction: Nanocrystalline Fe-Fe2O3 particle-deposited N-doped graphene as an activity-modulated Pt-free electrocatalyst for oxygen reduction reaction.

Correction for 'Nanocrystalline Fe-Fe2O3 particle-deposited N-doped graphene as an activity-modulated Pt-free electrocatalyst for oxygen reduction reaction' by Vishal M. Dhavale et al., Nanoscale, 2015, 7, 20117-20125.

Direct synthesis of a carbon nanotube interpenetrated doped porous carbon alloy as a durable Pt-free electrocatalyst for the oxygen reduction reaction in an alkaline medium

The carbon nanotube interpenetrated porous doped carbon alloy derived from trimetallic ZIF displays excellent oxygen reduction activity in alkaline media.

Ionic Liquid-Derived MoC Nanocomposites with Ordered Mesoporosity as Efficient Pt-Free Electrocatalyst for Hydrogen Evolution and Oxygen Reduction

1-butyl-3-methylimidazolium molybdate ionic liquids filled in mesopores of SBA-15 silica were successfully converted to MoC nanocomposites with about 5 nm particle size and ordered mesoporous channels, which were found to be efficient Pt-free bifunctional electrocatalysts for hydrogen evolution and oxygen reduction reaction.

High Performance Palladium Supported on Nanoporous Carbon under Anhydrous Condition.

Due to the high cost of polymer electrolyte fuel cells (PEFCs), replacing platinum (Pt) with some inexpensive metal was carried out. Here, we deposited palladium nanoparticles (Pd-NPs) on nanoporous carbon (NC) after wrapping by poly[2,2′-(2,6-pyridine)-5,5′-bibenzimidazole] (PyPBI) doped with phosphoric acid (PA) and the Pd-NPs size was successfully controlled by varying the weight ratio between Pd precursor and carbon support doped with PA. The membrane electrode assembly (MEA) fabricated from the optimized electrocatalyst with 0.05 mgPd cm−2 for both anode and cathode sides showed a power density of 76 mW cm−2 under 120 °C without any humidification, which was comparable to the commercial CB/Pt, 89 mW cm−2 with 0.45 mgPt cm−2 loaded in both anode and cathode. Meanwhile, the power density of hybrid MEA with 0.45 mgPt cm−2 in cathode and 0.05 mgPd cm−2 in anode reached 188 mW cm−2. The high performance of the Pt-free electrocatalyst was attributed to the porous structure enhancing the gas diffusion and the PyPBI-PA facilitating the proton conductivity in catalyst layer. Meanwhile, the durability of Pd electrocatalyst was enhanced by coating with acidic polymer. The newly fabricated Pt-free electrocatalyst is extremely promising for reducing the cost in the high-temperature PEFCs.

Single-Step Synthesis of W2C Nanoparticle-Dispersed Carbon Electrocatalysts for Hydrogen Evolution Reactions Utilizing Phosphate Groups on Carbon Edge Sites.

A novel, one-step protocol for the selective synthesis of W2C nanoparticles from phosphotungstic acid (H3PW12O40), a low-cost and commercially available tungsten compound, was developed. The nanoparticles had diameters of 1–50 nm and were dispersed on a carbon substrate. The W2C nanoparticles were prepared by a simple operation sequence, involving impregnation of carbon black with H3PW12O40 followed by calcination at 1000 °C. X-ray diffraction study revealed the selective formation of the W2C phase in the samples prepared, whereas the tungsten carbide (WC) phase was present in the control prepared from H2WO4. Stable W2C nanoparticles were obtained using this method owing to the presence of phosphate at the interfaces between the W2C nanoparticles and the carbon substrates, which inhibited the diffusion of carbon atoms from the carbon substrates to the W2C nanoparticles, leading to the formation of WC. The W2C nanoparticles prepared showed an excellent catalytic activity for the hydrogen evolution reaction (HER), with low Tafel slopes of ∼50 mV/decade. The HER catalytic activity was notably high, being comparable to that of MoS2, which is a promising alternative to Pt. The present method can potentially be applied to produce highly effective, low-cost, Pt-free electrocatalysts for the HER.

Galvanic exchange at layered doubled hydroxide/N-doped graphene as an in-situ method to fabricate powerful electrocatalysts for hydrogen evolution reaction

Introducing a novel strategy for growing dispersed metal nanoparticles at reduced graphene oxide (rGO) and nitrogen-doped GO (rNGO), this work aimed to design Pt-free electrocatalysts for water splitting. For this purpose, gold nanoparticles were fabricated by the in-situ galvanic exchange of layered double hydroxide (LDH) metals on rGO and rNGO. The significant roles of the galvanic exchange method, LaNi-LDH, and the Au nanoparticles synthesized on the rGO/rNGO-LaNi-LDH surface (Au@rGO/rNGO-LaNi-LDH) were investigated via a variety of methods and certain novel properties such as nitrogen-metal bridge bonds between the metal component of Au@LDH and the nitrogen component of rNGO were established, which indicated the semi-nanorod morphology of the Au@rGO/rNGO-LaNi-LDH thus produced. Electrochemical studies were used to reveal an onset potential of only −80 mV vs. RHE at an exchange current density of about 10 mA cm−2 with a small Tafel slope of 60 mV dec−1 for the hydrogen generation reaction in a 0.5 mol L−1 H2SO4 solution. The isolated island architecture of rNGO/LaNi-LDH and rNGO/Au@LaNi-LDH were found to promise rich and active sites to be exposed, which allow for the effective interaction of the reactants (e.g., protons) with these active sites.

Graphene sheets wrapped carbon nanofibers as a highly conductive three-dimensional framework for perpendicularly anchoring of MoS2: Advanced electrocatalysts for hydrogen evolution reaction

It is universally acknowledged that the development of high-efficiency Pt-free electrocatalysts for hydrogen evolution reaction (HER) is a challenging and demanding task nowadays. Herein, graphene wrapped carbon nanofiber @ molybdenum disulfide (GCNF@MoS2) hybrids with hierarchical structure have been successfully prepared as HER electrocatalysts through the combination of electrospinning, solution soaking and solvothermal methods. The wrapping of few-layered graphene functions crucially as a “bridge” closely linking three-dimensional (3D) carbon nanofibers and electrocatalytically active MoS2, providing a highly conductive pathway through the whole hybrids, thus facilitating the transport of electrons. Furthermore, carbon nanofibers acting as “spacers” between graphene layers can efficiently impede their restacking, thus giving full play to the superior electrical conductivity of graphene. Benefiting from the 3D network and template of GCNF, MoS2 nanosheets can grow densely and perpendicularly on the fiber surface, therefore exposing catalytically active edges effectively. Owing to the synergistic effects among three components, the GCNF@MoS2 hybrid exhibits remarkable electrocatalytic activity with a low onset potential of −0.08V, a small Tafel slope of 49.6mV per decade, a large current density (10.0mAcm−2 at η=0.15V) as well as excellent stability. Apart from fabricating an efficient HER catalyst, this work also provides a practical strategy for designing hybrid materials with multi-functions for their potential applications in new energy field.

Co@N-CNTs derived from triple-role CoAl-layered double hydroxide as an efficient catalyst for oxygen reduction reaction

Co nanoparticle-encapsulated N-doped carbon nanotubes (Co@N-CNTs) are prepared as a Pt-free electrocatalyst for oxygen reduction reaction (ORR) via direct pyrolysis of a CoAl-layered double hydroxide (CoAl-LDH)/melamine mixture. The approach could bundle the following distinct features: (i) commercially available melamine as both carbon and nitrogen bi-functional sources; (ii) scalably prepared CoAl-LDH precursor chosen to play a triple role in catalyzing the formation of N-CNTs and serving the electroactive Co nanoparticles, as well as in facilitating the growth of long N-CNTs owing to the confinement effect of the non-active Al2O3 matrix formed; (iii) an alternative to prepare one-dimensional length-and-performance-tunable N-CNTs, which are obtained typically by using catalytic chemical vapor deposition (CCVD) of two gaseous carbon and nitrogen resources on the surface of an LDH layer. The long Co@N-CNTs exhibits the highly enhanced electrocatalytic activity and stability for ORR (onset potential at 929 mV, half-wave potential at 849 mV vs. RHE, and limited current density at 6.0 mA cm−2). The CoAl-LDH precursor-based approach may open up a simple and feasible alternative to design and produce low-cost electrocatalysts for fuel cells.

Layer-by-Layer Self-Assembled Graphene Multilayers as Pt-Free Alternative Counter Electrodes in Dye-Sensitized Solar Cells.

Low cost, charged, and large scale graphene multilayers fabricated from nitrogen-doped reduced graphene oxide N-rGO(+), nitrogen and sulfur codoped reduced graphene oxide NS-rGO(+), and undoped reduced graphene oxide rGO(-) were applied as alternative counter electrodes in dye-sensitized solar cells (DSSCs). The neat rGO-based counter electrodes were developed via two types of layer-by-layer (LBL) self-assembly (SA) methods: spin coating and spray coating methods. In the spin coating method, two sets of multilayer films were fabricated on poly(diallyldimethylammonium chloride) (PDDA)-coated fluorine-doped tin oxide (FTO) substrates using GO(-) combined with N-GO(+) followed by annealing and denoted as [rGO(-)/N-rGO(+)]n or with NS-GO(+) and denoted as [rGO(-)/NS-rGO(+)]n for counter electrodes in DSSCs. The DSSCs employing new types of counter electrodes exhibited ∼7.0% and ∼6.2% power conversion efficiency (PCE) based on ten bilayers of [rGO(-)/N-rGO(+)]10 and [rGO(-)/NS-rGO(+)]10, respectively. The DSSCs equipped with a blend of one bilayer of [rGO(-):N-rGO(+)] and [rGO(-):NS-rGO(+)] on PDDA-coated FTO substrates were prepared from a spray coating and showed ∼6.4% and ∼5.6% PCE, respectively. Thus, it was demonstrated that a combination of undoped, nitrogen-doped, and nitrogen and sulfur codoped reduced graphene oxides can be considered as potentially powerful Pt-free electrocatalysts and alternative electrodes in conventional photovoltaic devices.

Efficient Pt-free electrocatalyst for oxygen reduction reaction: Highly ordered mesoporous N and S co-doped carbon with saccharin as single-source molecular precursor

Despite that nitrogen (N) and sulfur (S) co-doped ordered mesoporous carbon (OMC) as Pt-free catalyst for oxygen reduction reaction (ORR) shows a desirable performance, the synthesis method is always complicated and expensive, which greatly hinders its development and application. In the present work, a highly ordered mesoporous N and S co-doped carbon material is developed. The material is obtained by combining hard template and high-temperature pyrolysis method using cheap saccharin as a single-source molecular precursor, SBA-15 as the hard template and FeCl3 as the catalyst to promote the carbonization process. It is found that the as-prepared SN-OMC catalyst, compared with the commonly used commercial Pt/C (20wt.%), exhibits comparable ORR electrocatalytic activity with mainly four-electron (4e−) process, superior stability and inertness to methanol in alkaline media, which could mainly benefit from the highly ordered mesoporous structure and the synergistic effect caused by the dual N and S doping. These advantages render SN-OMC a promising ORR electrocatalyst and a cheap alternative to Pt/C for practical fuel cell applications.

Cotton Wool Derived Carbon Fiber Aerogel Supported Few-Layered MoSe2 Nanosheets As Efficient Electrocatalysts for Hydrogen Evolution.

Recent studies have proven that newly emerging two-dimensional molybdenum diselenide (MoSe2) is a promising noble-metal-free electrocatalyst for hydrogen evolution reaction (HER). Increasing the exposures of the active edges of MoSe2 nanostructures is a key issue to fully realize the excellent electrochemical properties of MoSe2. In this work, a few-layered MoSe2/carbon fiber aerogel (CFA) hybrids have been facilely obtained through the combination of high-temperature carbonization and one-pot solvothermal reaction. CFA derived from cotton wool is used as a three-dimensional conductive network for construction of hierarchical MoSe2/CFA hybrids, where few-layered MoSe2 nanosheets are uniformly and perpendicularly decorated on the surfaces of CFA. In the designed and prepared hybrids, CFA effectively increases the exposures of the active edges of MoSe2 nanosheets as well as provides reduced lengths for both electron transportation and ion diffusion. Therefore, the obtained optimal MoSe2/CFA hybrid exhibits excellent electrochemical activity as HER electrocatalyst with a small onset potential of -0.104 V vs reversible hydrogen electrode and a small Tafel slope of 62 mV per decade, showing its great potential as a next-generation Pt-free electrocatalyst for HER.

Density Functional Theory Study of Iron Phthalocyanine Porous Layer Deposited on Graphene Substrate: A Pt-Free Electrocatalyst for Hydrogen Fuel Cells

This paper details the use of ab initio density functional theory (DFT) to analyze a potential Pt-free catalyst, nonbonded iron phthalocyanine monolayer on graphene substrate (FePc/graphene), for an approximation of catalytic pathway and properties in oxidation reduction reaction of H2 and O2 to produce water. DFT calculations show that the associative mechanism, where O2 molecules chemisorbed on Fe site and prefer hydrogenation to O–OH intermediate species with ambient H+ and electron transfer followed by subsequent water formation reaction (WFR), is found to dominate for the FePc/graphene surface. Throughout the entire oxygen reduction reaction (ORR) process, the initial reduction of O2 to O–OH reaction appears to be the rate-limiting step with a reaction barrier of 0.68 eV. The complete free energy profile suggests that oxygen molecules are inherently favorable for reduction into water on FePc functionalized graphene surface.

Pyridine-functionalized graphene oxide, an efficient metal free electrocatalyst for oxygen reduction reaction

Here, a novel approach for the preparation of pyridine functionalized graphene nanosheets (Py-EGO) is developed. Using a simple thermal treatment, pyridine was linked to reduced graphene oxide using epoxy group or hydroxyl group that existing at a surface of the graphene. The electrochemical behavior of Py-EGO for the reduction of oxygen was studied. The results showed that the new nanocomposite has a powerful potential as an electrocatalyst for oxygen reduction reaction (ORR) especially compare to N-doped graphene oxide, in alkaline solution. In addition, the Py-EGO electrocatalyst exhibited tolerance to methanol crossover effect. The results of our studies indicate that Py-EGO has a better durability, much higher selectivity, much better electrochemical stability and high catalytic activity towards the ORR than that of commercial Pt/C electrocatalyst. The Pt-free electrocatalyst improves catalytic activity and reduce the cost of electrocatalyst for ORR. The proposed simple method for synthesize Py-EGO electrocatalyst promising its further application in fuel cells.

Pt-free silver nanoalloy electrocatalysts for oxygen reduction reaction in alkaline media

Silver nanoalloy electrocatalysts with comparable activity and better stability than commercial Pt/C for oxygen reduction reaction (ORR) in advanced metal–air batteries and fuel cells.

Inexpensive Ipomoea aquatica Biomass-Modified Carbon Black as an Active Pt-Free Electrocatalyst for Oxygen Reduction Reaction in an Alkaline Medium.

The development of inexpensive and active Pt-free catalysts as an alternative to Pt-based catalysts for oxygen reduction reaction (ORR) is an essential prerequisite for fuel cell commercialization. In this paper, we report a strategy for the design of a new Fe–N/C electrocatalyst derived from the co-pyrolysis of Ipomoea aquatica biomass, carbon black (Vulcan XC-72R) and FeCl3·6H2O at 900 °C under nitrogen atmosphere. Electrochemical results show that the Fe–N/C catalyst exhibits higher electrocatalytic activity for ORR, longer durability and higher tolerance to methanol compared to a commercial Pt/C catalyst (40 wt %) in an alkaline medium. In particular, Fe–N/C presents an onset potential of 0.05 V (vs. Hg/HgO) for ORR in an alkaline medium, with an electron transfer number (n) of ~3.90, which is close to that of Pt/C. Our results confirm that the catalyst derived from I. aquatica and carbon black is a promising non-noble metal catalyst as an alternative to commercial Pt/C catalysts.

Hollow core-shell structured Ni-Sn@C nanoparticles: a novel electrocatalyst for the hydrogen evolution reaction.

Pt-free electrocatalysts with high activity and low cost are highly pursued for hydrogen production by electrochemically splitting water. Ni-based alloy catalysts are potential candidates for the hydrogen evolution reaction (HER) and have been studied extensively. Here, we synthesized novel hollow core-shell structure Ni-Sn@C nanoparticles (NPs) by sol-gel, chemical vapor deposition, and etching processes. The prepared electrocatalysts with porous hollow carbon layers have a high conductivity and large active area, which exhibit good electrocatalytic activity toward HER. The Tafel slope of ∼35 millivolts per decade measured in acidic solution for Ni-Sn@C NPs is the smallest one to date for the Ni-Sn alloy catalysts, and exceeds those of the most non-noble metal catalysts, indicating a possible Volmer-Heyrovsky reaction mechanism. The synthetic method can be extended to prepare other hollow core-shell structure electrocatalysts for low-temperature fuel cells.

A Pt-free Electrocatalyst Based on Pyrolized Vinazene-Carbon Composite for Oxygen Reduction Reaction

The 2-vinyl-4, 5-dicyanoimidazole (Vinazene) was used as a nitrogen precursor to synthesize a promising non-precious metal (NPM) catalyst for oxygen reduction reaction (ORR). Vinazene together with an iron source was impregnated into a carbon matrix and pyrolyzed at 900°C in N2 atmosphere. The structure of the resulting Fe–N–C nanocomposite was analyzed by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. Both rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) experiments showed excellent ORR activity for the obtained catalyst with low H2O2 formation (∼3.0%) in 0.1M KOH. The catalyst was found to be rich in mesoporous structure along with high percentage of pyrrolic-N function with surface area of about 673m2g−1 and pore size of 4.2nm. In addition to its excellent ORR activity, the catalyst showed remarkable tolerance towards methanol oxidation and demonstrates good stability over 10,000 potential cycles (0.6–1.0V Vs RHE). We believe that this N-rich Vinazene molecule will be beneficial to further development of nitrogen doped carbon electrocatalysts.