Electrocatalysts

Direct methanol fuel cells (DMFCs) represent an interesting alternative in obtaining electricity in a clean and efficient way. Portable power sources are one of the most promising applications of passive DMFCs. One of the requirements in these devices is to use high alcohol concentration, which due to methanol crossover causes a considerable loss of fuel cell efficiency. In order to develop methanol tolerant cathodes with suitable activity, different supported catalysts namely PtCo/C and PtCoRu/C, were prepared either via ethylene glycol reduction (EG) with or without microwave heating assistance (MW) or via the alloy method, the latter followed by a thermal treatment in a reducing atmosphere (N2/H2). All cathode-catalysts were tested to determine the role of the components in simultaneously enhancing the oxygen reduction reaction (ORR) and discouraging the methanol oxidation reaction. According to the synthesis methodology, X-ray photoelectron spectra showed that the amount of metal oxides on the surface varies, being higher on the PtCo/C EG and PtCoRu/C EG catalysts. The electrochemical characterization of the catalysts was accomplished in a three electrodes electrochemical cell with a glassy carbon rotating disk electrode covered with a thin catalytic film as working electrode. To study the ORR and the influence of different methanol concentrations, linear sweep voltammetry and cyclic voltammetry were employed. The PtCo/C EG, with an important metal oxide amount on the surface, and the PtCoRu/C MW and EG electrodes, both with RuO2 on their surfaces, were the most tolerant to methanol presence.

The scarcity and high cost of commercial noble metal-based materials necessitate the need for synthesizing alternative electrocatalysts for oxygen evolution reaction (OER). Many efforts put in place in addressing this problem have resulted in huge successes by employing different routes for synthesizing electrocatalysts, using different families of atoms and compounds. In this regard, this review describes the conceptual study of OER and an overview of electrocatalytic kinetics and theoretical modeling for oxygen evolution reaction. For in-depth understanding, a comprehensive and general overview of the recent developments in the OER electrocatalysts and efficient methods of testing the stabilities of catalysts to obtain reliable results are given. The study also includes some tutorial manuals for describing various parameters needed in electrochemical OER processes. We do hope they will be the useful guiding principles for the newcomers in this field. Interestingly, the emphasis is focused on describing different families of compounds used to synthesize high-performance OER electrocatalysts: which include transition metal compounds, polyoxometalates, carbon nanotubes, single atoms, layered double hydroxide, and non-metal compounds. Conclusively, important future perspectives to foster the advancement of this field are discussed.

Investigation of the hydrogen oxidation reaction (HOR) in alkaline media has been pursued in the past few years side by side with the development of alkaline membrane fuel cells (AMFCs), also called anion exchange membrane fuel cells (AEM-FCs). In this communication, we present the synthesis, electro-chemistry and AMFC test of a platinum-free HOR catalyst. The anode catalyst is prepared by growing palladium nanoparticles onto nanoparticles of an oxophilic metal (nickel), resulting in nano-dispersed, interconnected crystalline phases of Ni and Pd. When used in the anode of a hydrogen/air AMFC, such Pd/Ni catalyst exhibits high HOR activity, resulting in record high performance for a platinum-free AMFC (0.4 A cm À2 at 0.6 V vs RHE). The enhancement of HOR catalytic activity vs. that observed at Pd (or Ni) alone is revealed directly in rotating disc electrode tests of this Pd/Ni catalyst that shows a significant negative shift (200 mV) of the onset potential for the HOR current vs. the case of Pd.

Pt-Ni supported on carbon (Pt-Ni/C) with
varying content of Ni were synthesized using an
organic precursor. As synthesized these electrocatalyst
were characterized by EDX and XRD for their
composition and structure. Methanol electro-oxidation
activities of these catalysts were evaluated by
preparing a porous gas diffusion electrode (PGDE)
and performing cyclic voltammetry in 0.5 M H2SO4
and 0.5 M H2SO4/1 M CH3OH medium. The results
showed that Ni containing Pt catalysts were more
active toward methanol electro-oxidation reaction
then plane Pt supported on carbon catalysts.

Most wet-chemical methods that synthesize metal nanoparticles (NPs) of a particular size and desired shape include the use of a stabilizing surfactant, such as poly(vinylpyrrolidone) (PVP). The latter has the ability to prohibit and/or promote surface sites from participating in electrocatalytic reactions, i.e. the methanol oxidation reaction (MOR). In light of our recent findings that adsorbed PVP can enhance the MOR on Pt NPs, a strong effort was made herein to separate the NP surface orientation effect from that of surface-bound PVP. We report the in situ ATR-SEIRAS (attenuated total reflection-surface enhanced infrared reflection absorption spectroscopy) and electrochemical (EC) studies of MOR and CO oxidation reaction (COR) performed on PVP-free cubic and octahedral/tetrahedral (O/T) Pt NPs that were obtained using an adapted liquid phase UV photo-oxidation (UVPO) technique. Transmission electron microscope (TEM) images showed no observable changes of shape and size after the elimination of the PVP, while the integrity of the atomic surface structure was further confirmed by the orientation-dependent EC stripping analysis of irreversibly adsorbed adatoms, i.e. Bi and Ge. The MOR activity was enhanced by the preferential surface orientation of the O/T Pt NPs compared to commercial Pt black and the cubic Pt NPs. The in situ ATR-SEIRAS measurements showed that the PVP-free Pt NPs adsorbed more bridge-bound gaseous CO than those with residual PVP and the weakly hydrogen-bound interfacial water played an important role for the orientation dependent enhancement in MOR activity. Additionally, the findings of this work are coupled with previously published investigations regarding the influence that PVP exerts on the ultimate activity of the Pt NPs, i.e., the adsorbed PVP enhances further the MOR activity on the O/T but suppresses it on the cubic Pt NPs.

Nanostructured Bismuth-based materials are promising electrodes for highly efficient electrochemical reduction processes such as hydrogen evolution reaction (HER). In this work, a novel sort of nanocomposite made up of partially reduced Bi2O3 into metallic Bi anchored on a 3D network of Ni-foam as a high-performance catalyst for electrochemical hydrogen reduction. The application of the hybrid material for HER is shown. The high catalytic activity of the fabricated electrocatalyst arises from the co-operative effect of Bi/Bi2O3 and Ni-foam which provides a highly effective surface area combined with the highly porous structure of Ni-foam for efficient charge and mass transport. The advantages of the electrode for the electrochemical reduction processes such as high current density, low overpotential, and high stability of the electrode are revealed. An overall comparison of our as-prepared electrocatalyst with recently reported works on related work is done.

Electrochemical reduction of water to hydrogen holds great promise for clean energy, while its widespread application relies on the development of efficient catalysts with large surface area, abundant exposed active sites and superior electron conductivity. Herein, we report a facile strategy to configure an electrocatalyst composed of cobalt phosphide and rhodium uniformly anchored on reduced graphene oxide for hydrogen generation. The hybrids effectively integrate the exposed active sites, electron conductivity and synergistic effect of the catalyst. Electrochemical tests exhibit that the catalyst shows superior hydrogen evolution reaction catalytic activity and stability, with a small Tafel slope of 43 mV dec −1. Over-potentials as low as 29 and 72 mV are required to achieve current densities of 2 and 10 mA cm −2 in 0.5M H 2 SO 4 , respectively. The hybrid constitution with highly active sites on conductive substrate is a new strategy to synthesize extremely efficient electrocatalysts. Especially, the efficient synergistic effect among cobalt phosphide, rhodium and reduced graphene oxide provides a novel approach for configuring electrocatalysts with high electron efficiency.

A sensitive and selective detection of dopamine (DA) by a sensor based on cobalt oxide (Co 3 O 4) nanograin-decorated reduced graphene oxide (rGO) composite modified glassy carbon electrode (GCE) is reported. The rGO-Co 3 O 4 nanograin composites are synthesized by a facile hydrothermal route and optimized by varying the contents of rGO (5.7, 7.4, 9.1 and 10.7 wt%, denoted as C1, C2, C3 and C4 respectively). The crystallinity of the composite is examined by X-ray diffraction (XRD). Raman spectrum revealed the successful reduction of graphene oxide (GO) into rGO. The surface morphology through field emission scanning electron microscopy (FESEM) revealed that the granular-shaped Co 3 O 4 are decorated on rGO matrix with an average particle size of ∼35 nm. For electrochemical oxidation of DA, glassy carbon electrode (GCE) is modified with nanocomposites. Cyclic voltammetric results show that C3 modified GCE exhibit enhanced electrocatalytic performance in terms of oxidation potential and peak current in comparison to those of bare GCE, Co 3 O 4 nanograins, C1, C2 and C4 modified GCE. The choronoamperometric studies indicate that C3 modified GCE exhibit a low detection limit of (S/N = 3) 0.277 M in the linear range of 1–30 M. In addition, C3 demonstrates good selectivity towards the detection of DA in the presence of a 100-fold higher concentration of ascorbic acid, glucose and uric acid as the interfering species. The electrochemical sensing studies suggest that 3D rGO-Co 3 O 4 nanograins endow excellent catalytic activity, high selectivity and sensitivity towards DA.

In this contribution, a reagent free glucose biosensor was prepared based on multi walled carbon nanotubes (MWCNTs) composite via the electrochemical method. The synthesized MWCNTs were in turn successfully optimized by the chemical vapor deposition (CVD) method. The glucose oxidase (GOx) was immobilized on a carbon nanotubes/gelatin (Gl) composite using the entrapment technique, with an 8.42 s(-1) direct electron transfer rate between GOx and MWCNTs/Gl, which was then drop-casted onto a glassy carbon electrode (GCE). The bioactivity of GOx on modified GCE was retained during the electrochemical reactions. The cyclic voltammetric results coupled with the chronoamperometric response and obtained from modified GCE indicated that a GOx/MWCNTs/Gl/GC electrode can be utilized as a glucose biosensor via its display of high sensitivity and stability. The biosensor exhibited a wide linearity range to 8.9 mM glucose, with the detection limit of 0.54 mM and a stability of 75.4% current diminish after 25 days. The proposed fabrication method of glucose biosensor was in line with the developments of electrochemical research for glucose determination of human serum in the context of electrochemical reactions. The results indicated that the biosensor possessed good stability and acceptable fabrication reproducibility.

Link to Full-Text Articles :
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Fused aromatic network (FAN) structures are a category of ordered porous polymers that permit the specific fusion of building blocks into extended porous network structures with designed skeletons and pores. One significant feature of FANs is that their structures can be tailorable with fused aromatic rings without rotatable single‐bond connectivity. As a result, the geometry and space orientation of the building blocks are easily incorporated to guide the topological expansion of the architectural periodicity. The variety of building units and fused linkages make FANs a promising materials platform for constitutional outline and functional design. The stably confined spaces of FAN architectures can be extended for the exchange of photons, ions, electrons, holes, and guest molecules, and exhibit customized chemical, electrochemical and optical properties. Herein, the main progress and advances in the field of 2D and 3D FANs and their utilization as a platform to develop efficient electrocatalysts for energy conversion and storage applications are summarized.

In an effort to rationally design economic electrocatalysts, zinc-substituted cobalt phosphate and pyrophosphate were prepared using facile template-free combustion synthesis. They act as efficient stable bifunctional electrocatalysts due to the tuning of oxygen affinity by zinc substitution and catalytically active cobalt sites. Exploiting their bifunctional activity, these cobalt (pyro)phosphates were incorporated into a zinc-air battery in an alkaline electrolyte. An exponential increase in energy demands and deteriorating environmental quality have put an unprecedented emphasis on clean (green) methods of energy harvesting and storage. 1-3 Due to the possibility of a highly efficient single-step conversion into electricity or heat, chemical energy is a popular candidate for energy storage. 4 In this conversion, oxidation of energetic compounds is ubiquitously exploited. 5,6 However, the dioxygen bond is extremely strong, thereby tremendously retarding the kinetics of the oxygen reduction reaction (ORR). 7,8 In particular , in hydrogen-based fuel cells and metal-air batteries, H 2 O or OH À is formed as a by-product of discharge. Its reversibility depends upon the reconversion of these products back to dioxygen through an oxygen evolution reaction (OER), the kinetics of which is hampered by a strong O-H bond. 9 Therefore , bifunctional catalysts, which can accelerate both these (ORR and OER) reactions, are crucial in developing recharge-able high-density fuel cells and metal-air batteries. 10,11 Pt-Based catalysts exhibit the best ORR activities followed by certain transition metal oxides, 12 whereas Ir and Ru based oxides constitute the benchmarks for OER catalysis. 13,14 However, their high cost and poor activity retention prevent the realization of economically viable systems. Inexpensive transition metals like Mn, Co and Ni have always been favourable candidates in the development of cost-effective catalysts due to their easily interconvertible oxidation states. 15,16 In particular, various Co-based materials have been reported to exhibit efficient bifunctional activity. On another note, transition metal-based phosphates are known for their substantial stability in alkaline media. 17-20 Following this clue, we attempted to design bifunctional electrocatalysts by employing Co-based phosphate polyanionic materials. Co 2 P 2 O 7 pyrophosphate has been earlier reported as an ORR catalyst. 21 Inspired by reports on cation substitution enhancing the catalytic activity in spinels, 22-24 we made an effort to modify the cobalt phosphates by divalent cation substitution. In this spirit, we probed the electrocatalytic activity of zinc-substituted cobalt phosphate and pyrophosphate made via a facile solution combustion synthesis strategy. 25 The substitution of Co 2+ ions (0.65 pm) by slightly larger Zn 2+ ions (0.74 pm) is expected to alter the lattice parameters 26 and the oxygen affinities of the Co-redox centres, resulting in a promising catalytic activity. For the first time, these compounds were observed to exhibit promising stable bifunc-tional electrocatalytic activities in alkaline media, leading to their application in Zn-air batteries. Two specific (pyro)phosphates ZnCo 2 (PO 4) 2 and ZnCoP 2 O 7 (here onwards referred to as ZCP and ZCP2 respectively) were prepared using solution combustion synthesis. 25 Details of synthesis and material characterization are provided in the ESI. † Rietveld analysis confirmed the formation of the desired end-products. Satisfactory refinement parameters were obtained for ZCP (w 2 = 3.476, R p = 0.69 and R wp = 0.89) and ZCP2 (w 2 = 5.355, R p = 0.67 and R wp = 1.00). The detailed crystallographic information for ZCP and ZCP2 is provided in the ESI † (Tables S1 and S2). Both these phosphate compounds assume monoclinic frameworks with P2 1 /n symmetry (Fig. 1). Rietveld refinement led to the lattice parameters of: a = 7.54992(17) Å, b = 8.3924(4) Å, c = 5.05512(16) Å and b = 94.3941(32)1 for ZCP (matching PDF of Co 3 (PO 4) 2 : 01-070-2080) and a = 6.9830(6) Å, b = 8.3392(6) Å, † Electronic supplementary information (ESI) available: Experimental details, structural details of ZnCo 2 (PO 4) 2 and ZnCoP 2 O 7 phosphates, XPS data, and a table enlisting a comparison of the electrocatalytic properties of various Co-based compounds. See

Nanostructured Bismuth-based materials are promising electrodes for highly efficient electrochemical reduction processes such as hydrogen evolution reaction (HER). In this work, a novel sort of nanocomposite made up of partially reduced Bi2O3 into metallic Bi anchored on a 3D network of Ni-foam as a high-performance catalyst for electrochemical hydrogen reduction. The application of the hybrid material for HER is shown. The high catalytic activity of the fabricated electrocatalyst arises from the co-operative effect of Bi/Bi2O3 and Ni-foam which provides a highly effective surface area combined with the highly porous structure of Ni-foam for efficient charge and mass transport. The advantages of the electrode for the electrochemical reduction processes such as high current density, low overpotential, and high stability of the electrode are revealed. An overall comparison of our as-prepared electrocatalyst with recently reported works on related work is done.

Oxygen reduction electrocatalysts based on the
monoethanolmine complexes {[CoEtm]2(l-Etm)4Ni(NO3)2}
and {[CoEtm]2(l-Etm)4Ni(NO3)2} ? activated carbon
AG-3 have been obtained by high-temperature synthesis.
The nature of active centers on the synthesized electrocatalysts
was described. Using potentiostatic and cyclic
potentiodynamic voltammetry, the kinetic characteristics of
catalysts in the oxygen electroreduction reaction were
determined. Thermal decomposition of the thermally
unstable complexes was described and character of the
active centers formed was discussed. The optimal synthesis
temperature of electrocatalysts is 600 C in an inert
atmosphere. The calculated exchange current densities for
the oxygen electroreduction reaction at the catalysts in 1 M
KOH at 20 C was j0 = 1.01 9 10-3 A g-1–3.3 9 10-3
A g-1. The Tafel slopes of stationary polarization curves
are 0.054–0.063 V for b1 and 0.106–0.125 V for b2. The
prepared electrocatalysts can be recommended only for
electrochemical systems with alkaline electrolyte.

Supported PtSnIr/C, PtSn/C, and IrSn/C catalysts with potential application in a direct alcohol fuel cell were prepared by chemical reduction employing Pechini methodology. The catalyst particles were characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS). Linear sweep voltammetry (LV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements were performed by using a glassy carbon working electrode covered with the catalyst in a 1 M ethanol + 0.5 M H2SO4 solution at 60 °C. It was demonstrated through XPS that PtSnIr/C and IrSn/C contain both IrO2 and SnO2. LV and chronoamperometry show a better catalytic behavior for ethanol oxidation on PtSnIr/C in the low-potential region and the improvement is attributed to the presence of both Sn and Ir oxides. The EIS accurately established that PtSnIr/C improved ethanol oxidation at lower potentials than PtSn/C.

In the present work, natural biomass and chemical materials were applied as the heteroatom resources for modifying the Porous Graphene (PG) structure by pyrolysis method at 900 ºC. The physical and chemical characterizatons were performed by means of Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), Raman Spectroscopy, N 2 Adsorption-Desorption, and X-ray Photo-electron Spectroscopy (XPS). Furthemore, the behavior of the prepared materials was investigated by Cyclic Voltammetry (CV) and Rotating Disk Electrode (RDE). The obtained results indicated that doping of heteroatoms into the graphene framework was possible using a low-cost and environment-friendly biomass material as well as chemical sources. Moreover, one-step quarternary and tersiary co-doped graphene could be acheived using natural biomass. The prepared electrocatalysts using grape leaves and sulfur trioxide pyridine complex exhibit higher electrocatalytic performance as exampled which conducted the electrocatalyst in 4epathway and showed high stability in methanol solutions during the process, confirming their considerable potential to Oxygen Reduction Reaction (ORR) as an electro-catalyst. Moreover, the onset potential of Gl300G-900 and GSP 900 (0.93 V vs RHE) is almost equal to the Pt/C 20 wt % (0.99 V vs RHE). These optimal prepared cathodes (Gl300G-900 and GSP 900) in the Microbial Fuel Cell (MFC) test lead to considerable power densities of 31.5 mW m-2 and 30.9.mW m-2 , which are close to 38.6 mW m-2 for the Pt/C 20 wt % cathode.

MoS2 becomes an efficient and durable nonprecious‐metal electrocatalyst for the hydrogen evolution reaction (HER) when it contains multifunctional active sites for water splitting derived from 1T‐phase, defects, S vacancies, exposed Mo edges with expanded interlayer spacings. In contrast to previously reported MoS2‐based catalysts targeting only a single or few of these characteristics, the all‐in‐one MoS2 catalyst prepared herein features all of the above active site types. During synthesis, the intercalation of in situ generated NH3 molecules into MoS2 sheets affords ammoniated MoS2 (A‐MoS2) that predominantly comprises 1T‐MoS2 and exhibits an expanded interlayer spacing. The subsequent reduction of A‐MoS2 results in the removal of intercalated NH3 and H2S to form an all‐in‐one MoS2 with multifunctional active sites mentioned above (R‐MoS2) that exhibits electrocatalytic HER performance in alkaline media superior to those of all previously reported MoS2‐based electrocatalysts. In particular, a hybrid MoS2/nickel foam catalyst outperforms commercial Pt/C in the practically meaningful high‐current region (>25 mA cm−2), demonstrating that R‐MoS2‐based materials can potentially replace Pt catalysts in practical alkaline HER systems.

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The anion exchange membrane fuel cell (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt-free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt-free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt-free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H 2 and pure air show peak power densities of more than 500 mW cm-2 .

Understanding the dynamics of water in solid-state polymer electrolytes (eg, Nafion) is important for a variety of applications ranging from membrane-based water purification to hydrogen fuel cells. In this study, the dynamics of water in Nafion was investigated at both ...