Powerful Electrocatalysts Research Articles

Ultrasound-Assisted Synthesis of High-Entropy Materials for Enhanced Oxygen Evolution Electrocatalysis

High-entropy materials (HEMs) play a significant role in the electrocatalytic oxygen evolution reaction (OER) due to their unique properties. However, there are still challenges in the preparation of HEMs for OER catalysts. In this study, the FeCoNiMnCr catalyst is synthesized for the first time using the ultrasonic hydrothermal-sintering technique and exhibits excellent performance for OER electrocatalysis. There is an optimal ultrasonic hydrothermal time and power for achieving the best OER performance. The results demonstrate that the performance of FeCoNiMnCr catalysts prepared through ultrasonic hydrothermal sintering (US-FeCoNiMnCr) is significantly improved compared with the traditional hydrothermal-sintering method. The US-FeCoNiMnCr catalyst exhibits an overpotential of 228 mV at the current density of 10 mA cm−2 and a Tafel slope as low as 45.39 mV dec−1 in an alkaline medium. Moreover, the US-FeCoNiMnCr catalyst demonstrates remarkable stability in electrocatalytic OER with a minimal potential increase observed even after 48 h. This work not only provides valuable insights into high-entropy material synthesis, but also presents a powerful electrocatalyst for water electrolysis.

Hydrogen spillover in Pt/Ni(OH)2/Mo2TiC2Tx electrocatalyst improves pH-universal hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction (HER) shows potential to transition from fossil fuels to green renewable energy. Designed for high efficiency and stability electrocatalyst in pH-universal electrolyte is of great significance but challenging. Herein, a novel electrocatalyst of two-dimensional (2D) Mo2TiC2Tx MXene supported Pt/Ni(OH)2 (denoted as Pt/Ni(OH)2/Mo2TiC2Tx) is reported by hydrogen spillover effect for efficient HER in the full-pH range. The operando electrochemical characterization reveals that the hydrogen spillover phenomenon interactions between multi-functional catalytic sites, e.g. Pt, Ni(OH)2 and Mo2TiC2Tx, are used to enhance HER performance and expedite HER kinetics. Moreover, theoretical calculation via density functional theory demonstrates the Pt/Ni(OH)2/Mo2TiC2Tx possess free energy of absorbed hydrogen close to zero (≈– 0.09 eV), which leads to optimal activity. As expected, the electrocatalyst necessitates the overpotential of 25, 33 and 36 mV at 10 mA cm−2 in acidic, alkaline, and neutral conditions, respectively, which are outperforming Pt/C. This work furtherly demonstrates a new way to design a powerful electrocatalyst for pH-universal HER based hydrogen spillover phenomenon.

Engineering organic polymers as emerging sustainable materials for powerful electrocatalysts.

Cost-effective and high-efficiency catalysts play a central role in various sustainable electrochemical energy conversion technologies that are being developed to generate clean energy while reducing carbon emissions, such as fuel cells, metal-air batteries, water electrolyzers, and carbon dioxide conversion. In this context, a recent climax in the exploitation of advanced earth-abundant catalysts has been witnessed for diverse electrochemical reactions involved in the above mentioned sustainable pathways. In particular, polymer catalysts have garnered considerable interest and achieved substantial progress very recently, mainly owing to their pyrolysis-free synthesis, highly tunable molecular composition and microarchitecture, readily adjustable electrical conductivity, and high stability. In this review, we present a timely and comprehensive overview of the latest advances in organic polymers as emerging materials for powerful electrocatalysts. First, we present the general principles for the design of polymer catalysts in terms of catalytic activity, electrical conductivity, mass transfer, and stability. Then, the state-of-the-art engineering strategies to tailor the polymer catalysts at both molecular (i.e., heteroatom and metal atom engineering) and macromolecular (i.e., chain, topology, and composition engineering) levels are introduced. Particular attention is paid to the insightful understanding of structure-performance correlations and electrocatalytic mechanisms. The fundamentals behind these critical electrochemical reactions, including the oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, oxygen evolution reaction, and hydrogen oxidation reaction, as well as breakthroughs in polymer catalysts, are outlined as well. Finally, we further discuss the current challenges and suggest new opportunities for the rational design of advanced polymer catalysts. By presenting the progress, engineering strategies, insightful understandings, challenges, and perspectives, we hope this review can provide valuable guidelines for the future development of polymer catalysts.

Metal-Free Covalent Organic Frameworks for the Oxygen Reduction Reaction.

The oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts that promote ORR, carbon-based metal-free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us in realizing the catalysts' design, the optimization of catalyst performance and the elucidation of structure-property relationship at the molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal-free electrocatalysts for the ORR due to their controlled skeletons, tailored pores size and environments, as well as well-defined location and kinds of catalytic sites. In this Concept article, the development of metal-free COFs for the ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge-sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospectives for designing and constructing powerful electrocatalysts based on the catalytic COFs.

Cu2 P7 -CoP Heterostructure Nanosheets Enable High-Performance of 5-Hydroxymethylfurfural Electrooxidation.

Electrooxidation of 5-hydroxymethylfural (HMF) into 2,5-furandicarboxylicacid (FDCA) has been regarded as a promising sustainable approach to achieve value-added chemicals. However, it is still impeded by the unsatisfactory performance of electrocatalysts. Here, Cu2 P7 -CoP heterostructure nanosheets were reported to enable powerful HMF electrooxidation. The Cu2 P7 -CoP heterostructure nanosheets were fabricated by microwave-assisted deep eutectic solvent (DES) approach, along with subsequent phosphiding. The Cu2 P7 -CoP heterostructure nanosheets enabled a superb 100 % HMF conversion at 1.43 V (vs. RHE) with 98.8 % FDCA yield and 98 % Faradaic efficiency (FE), demonstrating its promising application in HMF electrooxidation. X-ray photoelectron spectroscopy (XPS) analysis, open-circuit potential (OCP) approach and density functional theory (DFT) calculation uncovered that the electron transfer and redistribution between Cu2 P7 and CoP improved the adsorption capacity of HMF and modulated the catalytic performance. This study not only offered a powerful electrocatalyst for HMF electrooxidation, but also provided a conceptually new strategy for the heterostructure catalyst design.

Efficient Hydrogen Production at pH 7 in Water with a Heterogeneous Electrocatalyst Based on a Neutral Dimeric Cobalt-Dithiolene Complex

The development of efficient hydrogen production technologies is fundamental for replacing fossil-fuel-based energies. As such, electrocatalysts derived from Earth-abundant metal complexes are appealing, and interesting performances have typically been disclosed under acidic conditions in organic solvents. However, their applicability under relevant pH-neutral conditions has been underexplored. Herein, we demonstrate that nonionic, dimeric cobalt-dithiolene complexes supported on a multiwalled carbon nanotube (MWCNT)/carbon paper (CP) electrode are powerful electrocatalysts for hydrogen production in aqueous media at pH 7. The high turnover numbers encountered (TON up to 50980) after long reaction times (up to 16 h) are explained by the increased electroactive cobalt concentration on the modified electrode, which is ca. 4 times higher than that of a state-of-the-art cobalt porphyrin electrocatalyst. These findings point out that immobilizing well-defined, multinuclear, low-cost metal complexes on carbon material is a promising strategy to design highly electroactive electrodes enabling production of green energies.

Manganese, iron co-doped Ni2P nanoflowers as a powerful electrocatalyst for oxygen evolution reaction

MnFe-Ni 2 P/NF is synthesized by a simple hydrothermal and subsequent phosphorylation reaction. The prepared material has excellent OER activity with an overpotential of 220 mV at a current density of 10 mA cm −2 . • Trimetallic transition metal phosphide nanoflowers are in-situ synthesized on Ni foam. • The unique flower-like structure provides more active sites for the OER reaction. • MnFe-Ni 2 P/NF shows high catalytic stability for OER in alkaline media. • MnFe-Ni 2 P/NF shows higher catalytic activity than that of bimetallic phosphides. The development of abundant, high-performance electrocatalysts for oxygen evolution reactions (OER) is an ongoing challenge to renewable energy. Herein, we rationally synthesized a manganese (Mn) and iron (Fe) doped Ni 2 P nanosheet (MnFe-Ni 2 P) as a highly efficient electrocatalyst for OER in alkaline solution by a simple hydrothermal method and phosphorylation. The bimetal-doped phosphide nanosheets are directly grown on the conductive nickel foam (NF) to form a 3D structure which facilitates to expose active sites as much as possible. Due to the electron interaction between the Mn, Fe and Ni, which contributes to ion diffusion and gas release, trimetallic MnFe-Ni 2 P/NF delivers an extremely low overpotential of 220 mV at 10 mA cm −2 and a small Tafel slope of 53 mV dec −1 in alkaline electrolyte towards OER. Furthermore, the excellent stability of MnFe-Ni 2 P/NF lasts for at least 24 h at a high current density of 50 mA cm −2 without much deviation. We demonstrate that the trimetallic MnFe-Ni 2 P/NF benefits from the doping of Mn, Fe elements and the unique flower-like structure, exhibits more effective electrocatalytic activity compare to conventional noble metal catalysts and Ni 2 P series materials.

Rugae‐like N‐doped porous carbon incorporated with Fe‐N x and Fe 3 O 4 dual active sites as a powerful oxygen reduction catalyst for zinc‐air batteries

The sluggish kinetics of an air cathode has limited the wide application of zinc-air batteries. As novel powerful electrocatalysts, atomic Fe-N-C materials have attracted immense research interest. However, creating Fe-N-C and Fe3O4 dual-sites catalysts is still challenging. Here, we employ a facile and raw-material-sparse strategy to construct a zeolitic imidazolate frameworks (ZIF)-8-derived N-doped carbon catalyst configured by embedded Fe-Nx-C/Fe3O4 dual sites on highly flexible carbon clothe. By soaking the precursor in the iron solution followed by pyrolysis at an optimized temperature, Fe species can translate into dual sites. Our results reveal that the optimal Fe-NC-950 catalyst displays an impressive quasi-four-electron-transfer oxygen reduction reaction pathway exhibiting half-wave potential (E1/2) of 0.89 V and onset potential (Eonset) of 1.04 V. Moreover, Fe-NC-950 based zinc-air cell reached a high open-circuit voltage of 1.54 V and a power density of 165.0 mW cm−2. Our results also showed that the trace amount of Zn species inherited from ZIF-8 does not affect the catalyst performance.

Electrochemical Reduction of Nitrogen to Ammonia by Pd−S−Mo Nanosheets on a Hydrophobic Hierarchical Graphene Support

AbstractThe electrochemical nitrogen reduction reaction (ENRR) is regarded as a potential alternative to produce ammonia under ambient conditions. However, the lack of powerful electrocatalysts and the non‐negligible hydrogen evolution reaction (HER) have become a bottleneck of further development of ENRR. In this work, [Mo3S13]2− clusters were introduced onto 2D‐structured Pd nanosheets (NSs) to form Pd−S−Mo NSs with abundant Mo active sites for N2 activation. A Faradaic efficiency (FE) of 10.7 % was realized by Pd−S−Mo NSs on hydrophilic carbon support, superior to their single‐component counterparts. Furthermore, loading Pd−S−Mo NSs on hydrophobic hierarchical graphene support was carried out to suppress HER, achieving a FE of 23.8 % and improved ammonia yield. This work provides a designed principle of efficient ENRR electrocatalysts by engineering Mo active sites and catalyst supports.

Facile Fabrication of a Foamed Ag3CuS2 Film as an Efficient Self-Supporting Electrocatalyst for Ammonia Electrolysis Producing Hydrogen.

Ammonia (NH3) is one of the hydrogen carriers that has received extensive attention due to its high hydrogen content and carbon-free nature. The ammonia electro-oxidation reaction (AOR) and the liquid AOR (LAOR) are integral parts of an ammonia-based energy system. The exploration of low-cost and efficient electrocatalysts for the AOR and LAOR is very important but very difficult. In this work, a novel self-supporting AOR and LAOR bifunctional electrocatalyst of a Ag3CuS2 film is synthesized by a simple hydrothermal method. The Ag3CuS2 film without a substrate shows efficient catalytic activity and enhanced stability for NH3 electrolysis in both aqueous ammonia solution and liquid ammonia, including an onset potential of 0.7 V for the AOR and an onset potential of 0.4 V for the LAOR. The density functional theory calculations prove that compared to Cu atoms, Ag atoms with appropriate charge density on the surface of Ag3CuS2 are more electrocatalytically active for NH3 splitting, including the low energy barrier in the rate-determining *NH3 dehydrogenation step and the spontaneous tendency in the N2 desorption process. Overall, the foamed Ag3CuS2 film is one of prospective low-cost and stable electrocatalysts for the AOR and LAOR, and the self-supporting strategy without a substrate provides more perspectives to tailor more meaningful and powerful electrocatalysts.

Green application of trimetallic nickel-cobalt-molybdenum nanocomposites on 3D graphene oxide as a powerful electrocatalyst for hydrogen evolution reaction

In-situ designing of multiple metals electrocatalysts with high active sites and performance is the main challenge for hydrogen evolution reaction (HER). So in this work, 3D-rGO was easily obtained from 2D-graphene by a simple one-step hydrothermal method to create the interspace sites and active surface area. The Ni–Co–Mo tri-metallic@3D-rGO was synthesized and fully characterized by different techniques, e.g., FT-IR, XRD, Raman, FE-SEM, TEM, EDS, mapping, ICP-OES, AFM, voltammetry, and electrochemical impedance spectroscopy. According to the FE-SEM and TEM images, the Ni–Co–Mo tri-metallic@3D-rGO has a crumpled-formed structure. The as-prepared nanocomposite has high HER performance with a low potential of −0.11 (vs. RHE) to deliver 10 mA cm–2 and Tafel slope of 68 mV dec−1 for Pt and −0.25 V (vs. RHE) to deliver 10 mA cm−2 and Tafel slope of 110 mV dec−1 for graphite counter electrode. Furthermore, the 3D structure illustrates high long-term durability in the HER process for 1000 continuous cycles and 12 h operation at −0.42 V (vs. RHE) for Pt and graphite counter electrode. It's noticeable HER performance has the synergetic effect between 3D-rGO and tri-metallic structure with high porosity and electrical conductivity, enhancing HER kinetic.

Hydrodehalogenation of Polychloromethanes on Silver‐Based Gas Diffusion Electrodes

AbstractThis work reports the electroreduction of a volatile organic halide (trichloromethane) from an airborn stream. In the past years, we highlighted the role of polycrystalline silver as powerful electrocatalyst for the electroreductive hydrodehalogenation of volatile organic halides (VOH) in water/organic solvent mixtures, from 0 to 100 % of the aqueous component. The successful conversion of trichloromethane and 1,1,1‐trichloethane to the relevant dehalogenated compounds, methane and ethane have prompted us to extend the investigations to the treatment of gaseous effluents, adopting a silver Gas Diffusion Electrode (Ag‐GDE) and the appropriate cell design. In the field of electroreduction processes the possibility of using GDE to treat gaseous effluents for the removal of volatile organic pollutants represents an electrochemical challenge, and the treatment of N2/CHCl3 gas mixtures fed into the cathodic Ag‐GDE compartment demonstrates the feasibility of the electroreductive detoxification process. Our results will be presented and discussed in terms of CHCl3 removal efficiency, selectivity and energy consumption in preparative electrolyses.

Identification of catalytic sites for cerium redox reactions in a metal-organic framework derived powerful electrocatalyst

The development of N-doped carbon materials with highly catalytic activity for catalyzing electrode reactions as alternatives to noble metal is of great importance for the practical implementation of redox flow batteries (RFBs). However, in addition to C-Nx sites, the high structural heterogeneity of N-doped carbon materials often contains metal-Nx sites and graphene encapsulated metal nanoparticle simultaneously, as a result of their metal-assistant synthesis method. Thus it is challenging to identify the predominant active structure within N-doped carbon catalysts for RFBs, which normally receives far less attention in the field of RFB research. Herein, we report a general metal-organic frameworks assisted approach to high-yield growth of nitrogen-doped carbon nanotubes (NCNTs) onto 3D graphite felt (GF) substrates without the requirement of any additional C and N sources or costly and complex CVD systems. The obtained NCNTs-modified GF (NCNT-GF) exhibits high electrocatalytic activity and stability toward cerium redox reactions. Based on the moderate and selective NH4Cl-purification process and the electrochemical poison experiments, we definitely elucidate the spectator role of atomically dispersed metal-Nx sites and graphene encapsulated metal nanoparticles, and the pivotal role of C-Nx sites in the NCNT-GF materials for cerium redox reactions.

Pt-Pd-doped NiO nanoparticle decorated at single-wall carbon nanotubes: An excellent, powerful electrocatalyst for the fabrication of An electrochemical sensor to determine nalbuphine in the presence of tramadol as two opioid analgesic drugs

In this study, a Pt-Pd-doped NiO nanoparticle decorated at the surface of single-wall carbon nanotubes (Pt-Pd/NiO-NPs/SWCNTs) was synthesized using a simple chemical precipitation method and characterized by XRD, TEM, and EDS methods. The results confirmed that Pt-Pd/NiO-NPs/SWCNTs were synthesized with good purity and at the nanoscale size. Moreover, a highly sensitive electroanalytical sensor was fabricated by incorporating synthesized Pt-Pd/NiO-NPs/SWCNT nanocomposites into a carbon paste electrode (CPE) in the presence of 1-ethyl-3-methylimidazolium methanesulfonate (EMICH3SO3−) as binder. The Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE showed a powerful electro-catalytic activity for electro-oxidation of nalbuphine, and the results confirmed that the oxidation of nalbuphine was improved 6.34 times and relative oxidation potential was decreased about 110 mV compared to unmodified electrodes. The Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE also showed good catalytic activity for the determination of nalbuphine in the presence of tramadol and the oxidation potential of these opioid analgesic drugs separated with ΔE =460 mV. In the final step, the Pt-Pd/NiO-NPs/SWCNTs/EMICH3SO3−/CPE was used to determine nalbuphine with a detection limit of 0.9 nM and tramadol with a detection limit of 50.0 nM in drug samples. The results confirmed the powerful and interesting ability of the sensor in the analysis of a real sample.

Efficient electron transmission in covalent organic framework nanosheets for highly active electrocatalytic carbon dioxide reduction

Efficient conversion of carbon dioxide (CO2) into value-added products is essential for clean energy research. Design of stable, selective, and powerful electrocatalysts for CO2 reduction reaction (CO2RR) is highly desirable yet largely unmet. In this work, a series of metalloporphyrin-tetrathiafulvalene based covalent organic frameworks (M-TTCOFs) are designed. Tetrathiafulvalene, serving as electron donator or carrier, can construct an oriented electron transmission pathway with metalloporphyrin. Thus-obtained M-TTCOFs can serve as electrocatalysts with high FECO (91.3%, −0.7 V) and possess high cycling stability (>40 h). In addition, after exfoliation, the FECO value of Co-TTCOF nanosheets (~5 nm) is higher than 90% in a wide potential range from −0.6 to −0.9 V and the maximum FECO can reach up to almost 100% (99.7%, −0.8 V). The electrocatalytic CO2RR mechanisms are discussed and revealed by density functional theory calculations. This work paves a new way in exploring porous crystalline materials in electrocatalytic CO2RR.

Regulating the electronic structure of CoMoO4 microrod by phosphorus doping: an efficient electrocatalyst for the hydrogen evolution reaction.

It is of extreme importance to design efficient electrocatalysts for hydrogen evolution reaction (HER), which is considered as a promising approach to provide efficient and renewable clean fuel (hydrogen). Tuning the electronic structure through heteroatom doping demonstrates one of the most effective strategies to promote the electrocatalytic performance of HER. Herein, phosphorus-doping modulation is utilized to fabricate monoclinic P-CoMoO4 with optimized electron structure supported on nickel foam (P-CoMoO4/NF) for alkaline HER via a facile hydrothermal method, followed by low-temperature phosphidation. Notably, P-CoMoO4/NF shows outstanding electrocatalytic performance for HER in 1 M KOH with a low overpotential of 89 mV at 10 mA cm-2, a remarkable Tafel slope value of 59 mV dec-1, and excellent 24 h-long stability. The excellent catalyst activity and stability merits of P-CoMoO4/NF are comparable to the reported highly efficient non-precious metal HER electrocatalysts and could be applied as a powerful electrocatalyst in water electrolysis. This work provides a superior synthesis strategy for the effective design and rational fabrication of low-cost, highly active, and highly stable non-precious metal HER electrocatalysts for electricity-to-hydrogen applications.

Towards efficient oxygen reduction reaction electrocatalysts through graphene doping

The incessant and drastic growth of global energy demand make it imperative to develop new affordable high-quality materials at a large scale to act as powerful electrocatalysts (ECs) on the relevant energy reactions.Here, we report the synthesis and characterization (FTIR, Raman, XPS, XRD, TEM and SEM) of new engineered electrocatalysts based on situ co-precipitation of Co3O4 or Mn3O4 nanoparticles in the presence of N, S-doped graphene (Co/N3S3-GF and Mn/N3S3-GF). The nitrogen, sulphur dual-doped graphene was achieved by a scalable dry ball-milling procedure followed by thermal treatment using graphene flakes as carbon source and trithiocyanuric acid as the precursor.The three materials prepared were applied as electrocatalysts for the oxygen reduction reaction (ORR) and demonstrated excellent electrocatalytic performance in alkaline medium with Co/N3S3-GF and Mn/N3S3-GF presenting onset potentials of 0.87 V vs. RHE. These were comparable to Pt/C onset potential (0.91 V). All materials showed good diffusion-limiting current densities (−3.49 to −4.17 mA cm−2) and selectivity for the 4-electron O2 reduction to H2O. Furthermore, the Co/N3S3-GF and Mn/N3S3-GF electrocatalysts presented good tolerance to methanol poisoning and good stability with current retentions (76–81%).The approach followed in this work showed that affordable, simple and scalable procedures can be applied to develop ORR electrocatalysts with enhanced performances.

Phosphorus-doped carbon nitride as powerful electrocatalyst for high-power vanadium flow battery

The poor hydrophilicity and weak activity of graphite felt (GF) electrodes hinder the efficient application of vanadium flow batteries (VFB). Therefore, enhancing the electrolyte wettability and electrochemical activity of GF is an effective way to improve the energy efficiency (EE) and power density of VFB. In this work, we report a simple and environmental friendly method to prepare phosphorus-doped carbon nitride modified GF (P-C3N4@GF) electrode, in which the P-C3N4 electrocatalysts are homogeneously distributed on the surface of GF. Owing to the excellent electrolyte wettability and notable electrocatalytic activity, the as-prepared P-C3N4@GF electrode exhibits significantly enhanced electrochemical activity towards VO2+/VO2+ and V2+/V3+ redox couples. As a result, the VFB single cell with P-C3N4@GF electrode demonstrates outstanding rate performance at current densities of 50–300 mA cm−2. Specifically, a maximum power density of 616.2 mW cm−2 is achieved. Moreover, the P-C3N4@GF electrode exhibits superior stability and durability at a high current density of 150 mA cm−2. Based on the above results, the possible catalysis mechanisms of P-C3N4@GF towards positive and negative reactions of VFB are discussed.

NiO nanoparticles decorated at Nile blue-modified reduced graphene oxide, new powerful electrocatalysts for water splitting

New nanocomposites, containing nickel oxide nanoparticles (NiONPs) and Nile blue@reduced graphene oxide (NB/rGO), were synthesized. Nile blue was decorated on the surface of rGO by covalent bonds (using diazonium reaction). Then, NiONPs was immobilized on the surface of the functionalized rGO. The electrocatalytic and electrochemical behaviors of NiO@rGO and NiO@Nile/rGO nanocomposites for HER were investigated using cyclic voltammetry and electrochemical impedance spectroscopy in acidic and alkaline media. From them, NiO@rGO has shown long-term stability for HER in acidic solution at room temperature. The electrocatalytic activity of NiO@rGO (vs. NiO@Nile/rGO) for HER was greatly improved and its behavior was close to the behavior of platinum. In the next stage of our study, due to the importance of oxygen as an energy source, the production of oxygen molecules through electrochemical oxidation of water at NiO@rGO and NiO@Nile/rGO were studied too. For this purpose, the electrochemical behaviors of the nanocomposites for oxygen evolution reaction were investigated using cyclic voltammetry and electrochemical impedance spectroscopy in acidic and alkaline media. The results of them confirmed that NiO@Nile/rGO acts as an excellent electrocatalyst with good long-term stability for oxygen evolution reaction in 0.5 mol L−1 KOH solution at room temperature.Therefore, NiO@rGO and NiO@Nile/rGO can be used as powerful cathode and anode, respectively in an electrochemical cell for water splitting.

Local Surface Structure and Composition Control the Hydrogen Evolution Reaction on Iron Nickel Sulfides.

In order to design more powerful electrocatalysts, developing our understanding of the role of the surface structure and composition of widely abundant bulk materials is crucial. This is particularly true in the search for alternative hydrogen evolution reaction (HER) catalysts to replace platinum. We report scanning electrochemical cell microscopy (SECCM) measurements of the (111)-crystal planes of Fe4.5 Ni4.5 S8 , a highly active HER catalyst. In combination with structural characterization methods, we show that this technique can reveal differences in activity arising from even the slightest compositional changes. By probing electrochemical properties at the nanoscale, in conjunction with complementary structural information, novel design principles are revealed for application to rational material synthesis.