bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Electrochemistry at Metal-Oxide Interfaces: At the Crossroads of Activity and Stability
Authors: Markovic Nenad M 
Published: February 2020

The identification of materials needed for efficient energy conversion and fuel production in electrochemical systems must be guided by two equally important fundamental properties: optimization of their catalytic behavior and their long-term stability in hostile electrochemical environments. This is especially true for the oxygen evolution reaction (OER), the anodic-half cell reaction that takes place at high overpotentials on oxidized metal surfaces in hydrogen-oxygen electrolyzers, metal air batteries and electrometallurgy. The kinetics of the OER have, for the most part, been closely tied to the concept of the volcano plot, which generally expresses the rate of the OER as a function of more fundamental properties of the oxide materials, known as descriptors. These analyses showed that the interaction between the substrate and the reactants, intermediates, and the products has to be optimized for the reaction to proceed efficiently. Although concepts resulting from volcano plot analyses have led to the establishment of important catalytic trends, many fundamental questions still remain open. One key question is what relationship exists between the kinetics of the OER and the stability of oxide materials. The lack of understanding of such stability-activity relationships derives mainly from the fact that research directed to the development of anode materials for the OER has been strongly “activity-centric”, while almost completely ignoring the stability of active components during the OER.
Here, we show that this disparity in focus has masked the inherently close ties that exist between the stability and activity of monometallic and complex oxide catalysts. By studying the stability-activity relationships of well-characterized oxide surfaces, we demonstrate that there is a fundamental link between the stability of catalysts and their reactivity for the OER. This trend is observed for many oxide catalysts in both acidic and alkaline electrolytes, indicating that the stability-activity relationship is independent of the specific ionic/molecular species mediating the OER (i.e. OH- vs. H2O). We found that the degree of stability is always inversely proportional to activity and that stable surfaces are, in fact, not reactive.
Electrochemical Deposition of Pt Nanoclusters on WC for Hydrogen Evolution Reaction in Acid
Authors: Liu Yihua , Kimmel Yannick C. , Esposito Daniel , Chen Jingguang , Moffat Thomas , You Hoydoo 
Published: February 2020

Water splitting by electrolysis is an effective and renewable way to produce hydrogen fuel from acid or alkaline electrolytes. Presently, alkaline water electrolyzers are being the most widely employed, largely due to the use of low-cost catalysts. Yet, there is strong interest for expanded use of acid water electrolyzers in future because of better device performance than the alkaline. In this work, we explore and develop new fabrication techniques that could minimize the use of the Pt catalyst that is highly active, but too expensive to be used for hydrogen evolution reaction (HER) in acid water electrolyzers. Of our particular interest is to grow Pt monolayer films and nanostructures on tungsten carbide (WC) supports by electrodeposition.
Fig. 1 shows Pt deposition as a function of applied potential from a NaCl-supporting electrolyte. An interesting finding is that the deposition of Pt is prevented at potentials below -0.5 V, in spite of high driving forces for Pt clusters to form and grow. This talk will present ways in which this anomalous deposition behavior can be exploited for preparing novel Pt catalysts. A brief summary will be given for Pt deposition on Au [[1]] and Ni [[2]] electrodes where a monolayer-thick Pt film is deposited at -0.8 V but additional growth is quenched. For WC substrates, we will discuss challenges associated with the lack of Pt depositing at -0.80 V, before introducing to a new approach that is developed to facilitate the formation of Pt nuclei.
The proposed method involves cycling the potential between -0.8 V and -0.45 V at a fast rate of 50 mV/s. As shown in Fig. 2, Pt nanoclusters with high particle density could be grown on WC, and their average size is about 5 nm. To gain mechanistic insights on Pt nanostructure nucleation and growth, the deposits were analyzed using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and underpotentially deposited (UPD) hydrogen and copper. Correlations between deposition potential cycle and particle growth and particle density will be discussed.
Finally, Pt deposits were examined as catalysts for HER in 0.5 M sulfuric acid. The dependence of HER activity on the number of deposition cycles is shown in Fig. 3 where the HER activity approaches that of bulk platinum as the deposition cycles increase even though the expected total amount of platinum is far less than a complete coverage. This work illustrates that electrodeposition provides a simple and scalable way for preparing Pt nanocluster/WC catalysts, which exhibit high activity and durability toward HER in acid media.

[1] Y. Liu, D. Gokcen, U. Bertocci, T. P. Moffat, Science, 338, 1327 (2012).
[2] Y. Liu, C. M. Hangarter, D. Garcia, T. P. Moffat, Surf. Sci. (2014) dx.doi.org/10.1016/j.susc.2014.06.002

Figure 1
Photoelectrochemical Phenomena at Nano-V2O5 Films Impregnated with Bi3+
Authors: Mascaro Lucia Helena , Gromboni Murilo Fernando , Marken Frank , Downeey Elisabeth 
Published: February 2020

In the last two decades, the development of nanoscience and technology developed several nanostructures at different forms, such as nanoparticles, nanowires, nanotubes and nanoribbons. These materials offer a high potential for improving properties and can be used in many fields such as microelectronics, batteries, photovoltaic and photocatalytic devices. Vanadium oxides belong to the important class of 3d transition metals, with various electric, magnetic and structural properties, making these materials attractive for many industrial applications. This study aimed to obtain and characterize vanadium oxide films on titanium from ammonium metavanadate and then modify it by impregnation with Bi (III). The vanadium pentoxide was synthesized on Ti substrates by painting the surface with a suspension of 250 mg ammonium metavanadate in 5 ml of polyethylene glycol (PEG-300). The coated Ti plate was then heated at 400, 500 or 600 °C for one hour. Subsequently, the film obtained was impregnated with Bi (III) for 120 minutes under constant stirring, using 50 mL of a solution 10 mmol L-1 of bismuth nitrate at nitric acid. Then the samples were again annealed for one hour at the same temperature. The films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible spectroscopy and photoelectrochemical. From SEM analysis was possible to observe, after impregnation of Bi(III), the growing of long crystals on V2O5 films at 400 and 500 °C, while for the sample to 600 °C a globular structure was preferentially deposited on the tip of V2O5 crystals. Through EDS analysis it was observed that the sample obtained at 500 °C is that has the highest amount of Bi in the composition. The mapping by EDS showed that the elements were distributed over all surface. From XRD analysis the presence of V2O5 orthorhombic phase and monoclinic BiVO4 was detected. Band-gap calculated for the samples before and after impregnation also proved that V2O5 was converted to BiVO4, since the value before impregnation was 2.20 eV and after impregnation showed a value of 2.42 eV. The photocurrent value obtained for nano-V2O5 films impregnated with Bi3+ at 500 °C was 5 times higher than pure BiVO4 films. The results showed that it has been possible obtain a nanostructured V2O5 / BiVO4film on Ti substrate which is photoactive and could be used both in photoelectrocatalytic water as oxidation of organic molecules.
Acknowledgements: FAPESP 2012/23422-5 and CAPES.
Selective Oxygen Reduction to Hydrogen Peroxide Using Earth-Abundant Metal Pyrites As High-Performance Electrocatalysts
Authors: Ying Diwen , Ding Qi , Jin Song 
Published: February 2020

It is important to develop alternative catalysts made of inexpensive and earth-abundant elements with high catalytic activity and stability to replace the noble metal catalysts in various environmental1 and renewable energy applications.2 Here we report earth-abundant metal pyrites MS2 (M as Fe, Ni, and Co) as high performance electrocatalysts3,4 for oxygen reduction reaction (ORR) that is selective for generating hydrogen peroxide. In neutral solution of 0.1 M sodium perchlorate and acidic solution of 0.1 M perchloric acid, all three MS2 show high ORR catalytic activity with excellent Tafel slopes. Based on Koutecky-Levich (K-L) analysis, all MS2 and noble metal show similar potential-dependent selectivity of the two-electron peroxide pathway in neutral condition, and CoS2 is the best among metal pyrites in terms of the positive potential for 50% H2O2selectivity. The stability of metal pyrites is quite good in under ORR operation in both neutral and acidic solutions. These inexpensive metal pyrites are excellent ORR catalysts for selective peroxide generation and could find promising applications in environmental and renewable energy technologies.
1. X.-W. Liu; W.-W. Li; H.-Q. Yu; “Cathodic catalysts in bioelectrochemical systems for energy recovery from wastewater” Chem. Soc. Rev., 2014, 43, 7718-7745.
2. Matthew S. F.; Song Jin; “Earth-abundant inorganic electrocatalysts and their nanostructures for energy conversion applications” Energy Environ. Sci., 2014, 7, 3519-3542.
3. Matthew S. F.; Mark A. L.; Qi Ding; Nicolas S. K.; Song Jin; “Earth-Abundant Metal Pyrites (FeS2, CoS2, NiS2, and Their Alloys) for Highly Efficient Hydrogen Evolution and Polysulfide Reduction” J. Phys. Chem. C, 2014, 118 (37), 21347-21356.
4. Matthew S. F.; Rafal D.; Mark A. L.; Nicholas S. K.; Qi Ding; Song Jin; “High-Performance Electrocatalysis Using Metallic Cobalt Pyrite (CoS2) Micro- and Nanostructures” J. Am. Chem. Soc., 2014, 136 (28), 10053-100061.

Figure 1
Metal-Metal Bonding Dynamics of Anode Materials for Oxygen Evolution Reaction (OER) in Basic Electrolyte Studied By Using in Situ Surface Stress Measurements
Authors: Hoang Thao Thi Huong , Cohen Yair , Gewirth Andrew A. 
Published: February 2020

The electrochemical splitting of water offers an attractive way to provide a carbon-free source of hydrogen, however the efficiency is limited primarily by the overpotential of the anodic oxygen evolution reaction (OER, 4OH-→ 2H2O + 4e- + O2).1

Knowledge of oxide formation prior and during the OER is essential for understanding the mechanism and electrocatalysts. Extensive studies on the composition and morphology of metal and oxide electrodes in the OER by Raman,2 XAS,3 and QCM4have been reported. However, there is no reported technique to directly interrogate the oxide film during potential cycling or its evolution over time and multiple electrochemical cycles.
In this work, in situ electrochemical stress measurements are used to interrogate changes in oxide structure before and during the oxygen evolution reaction (OER) from Ir, Ni, Co, Au, and Pt electrodes in alkaline electrolyte. Stress evolution during potential cycling reports on changes in oxidation state and oxide forms. Hysteresis observed in the potential - dependent stress from Ir, Au, and Pt electrodes is associated with chemical irreversibility in electrode composition and roughness. Alternatively, Ni and Co exhibit reversible conversion between hydroxide and oxyhydroxide forms during cycling. From the experimentally determined stress, charge passed during electrode oxidation, and Young’s modulus, the change in strain exhibited by Ni and Co electrodes during hydroxide-oxyhydroxide conversion is calculated to be 7.0% and 8.4%, respectively. We also show that the magnitude of change in stress is proportional to the amount of material that is further oxidized. The similarity between processes yielding higher oxides and those involved with the OER mechanism yields are a rough correlation between film thickness and OER onset.5

Finally, we report the effect of electrodeposition additives to modify electrodeposited OER-active films to achieve high electrocatalyst efficiency for this reaction.
References
(1) Matsumoto, Y.; Sato, E. Materials Chemistry and Physics
1986, 14, 397-426.
(2) Desilvestro, J.; Corrigan, D. A.; Weaver, M. J. J Electrochem Soc
1988, 135, 885-892.
(3) Totir, D.; Mo, Y.; Kim, S.; Antonio, M. R.; Scherson, D. A. J Electrochem Soc
2000, 147, 4594-4597.
(4) Mo, Y.; Hwang, E.; Scherson, D. A. J Electrochem Soc
1996, 143, 37-43.
(5) Hoang, T. T. H.; Cohen, Y.; Gewirth, A. A. Analytical Chemistry
2014, 86, 11290-11297.
In Situ Reactive Imaging of Photoassisted Water Splitting Reaction Intermediates on n-Doped Strontium Titanate Using Surface Interrogation Scanning Electrochemical Microscopy
Authors: Simpson Burton H , Zhou Xuan , Rodríguez-López Joaquín 
Published: February 2020

Scanning electrochemical microscopy (SECM) gives spatially resolved information about electrochemical reactions occurring on surfaces, and easily probes reaction mechanisms. The in situ surface study of photoelectrochemical processes, such as water splitting at semiconductor electrodes, is challenging due to its fast kinetics and the multiple reactive intermediates formed. By combining the surface interrogation mode (SI-) of SECM [1] with transport simulations, the reactivity of multiple adsorbed intermediates resulting from water splitting on gently n-doped strontium titanate (STO) was investigated. Using this technique, we addressed the in situ detection of long lived holes and photogenerated hydroxyl radical on STO. Combined with the measurements on the local production of oxygen using the collection mode of SECM, our methodology provides an integrated view of reactivity at photocatalytic surfaces.
In our SI-SECM measurements, a micro- or nano-electrode used as SECM tip was positioned close to the STO surface and activated to generate a redox titrant that provided information about the surface coverage and reaction kinetics of adsorbed intermediates. By addressing different parts on the electrode surface, it is possible to obtain information about different surface condition son the STO electrode. This combined methodology brings spatial resolution to SI-SECM, and measured different adsorbate coverage on pristine and defective STO (100) surfaces. For the first time, SI-SECM was adapted to the reactive imaging of adsorbates to show how these affect photocatalytic performance on a heterogeneous surface.
[1] Rodríguez-López, J. The Surface Interrogation Mode of Scanning Electrochemical Microscopy (SI-SECM): an approach to the study of adsorption and (electro)catalysis at electrodes. In Electroanalytical Chemistry, a series of advances. Vol. 24. Bard, A.J. and Zoski, C.G., Eds. 2012, CRC Press, pp. 287-352.
A New Family of Catalysts for Production of Solar Fuels
Authors: Hupp Joseph T. 
Published: February 2020

Nature uses a variety of transition-metal containing, cluster-based cofactors to catalyze water oxidation, carbon dioxide reduction, and hydrogen evolution. Efforts to mimic Nature by constructing artificial catalytic clusters are often complicated either by catalyst aggregation and inactivation, or poor catalytic activity due to blocking of catylst active-sites by ligands needed for cluster stabilization or immobilization. We have developed a route to catalytic clusters of well-defined and pre-determined size and composition that is based on deploying atomic layer deposition on electrode-supported arrays of metalloporphyrins, or within appropriately designed, mesoporous metal-organic framework materials. This approach avoids the complications of both catalyst aggregation and ligand inactivation, while setting the stage for systematic, hypothesis-driven investigations of catalyst size/activity and composition/activity relationships.
Our focus thus far has been chiefly on transition-metal oxides and transition-metal sulfides. This talk will present the general approach to catalyst synthesis, as well as some representative findings for water oxidation,water reduction, or CO2 reduction.
Enhanced Low Bias Performance in Textured BiVO4 Photoanodes through Halide and Phosphate Treatments
Authors: Nair Vineet Vijayakrishnan , Perkins Craig L , Law Matt 
Published: February 2020

Over the last couple of years, BiVO4 has merged as a promising photoanode material owing to its earth abundance, suitable band gap (2.4eV), high absorption coefficient and a reasonable hole diffusion length (100nm)[1]. The intrinsic electron mobility has been shown to be a bottleneck[2] in achieving high photocurrents with a standalone BiVO4 photoanode. Recently photocurrents as high as 5mA/cm2 at OER have been demonstrated using a heterojunction with WO3 rods[3]. This however does not solve the intrinsic electron transport problems of BiVO4 and hence enhancing the photoresponse at relatively low biases close to the flatband potential still remains a challenge and limits its application in a high efficiency tandem device. Here we report photocurrents in excess of 3mA/cm2 at applied biases as low as 0.6V vs RHE with an onset potential of 0.19V vs RHE for sulfite oxidation.
A common route to improving the elctronic performance of BiVO4 is via addition of W or Mo as dopants. However, the addition of both W and Mo always results in an anodic shift in the onset potential, limiting the photoresponse at lower biases. In the this study, phosphate-based treatments of the fluorine-doped tin oxide are shown to eliminate the small rectifying junction existing at the back contact with BiVO4. Simultaneously, halide treatments were used to improve electron transport in undoped –BiVO4. Using results from our previous work[4], we have been able to successfully texture 300nm thin films with the previously mentioned phosphate and halide treatments to unity carrier separation at OER and over 80% at 0.6V RHE. Owing to the {004} texturing, these devices also demonstrate a record high catalytic activity for a standalone BiVO4 photoanode towards oxygen evolution. Such high carrier separation was achieved via halide treatment as well as surface texturing which reduces the density of in-gap surface defects states. UPS and XPS measurements were used to ascertain the nature and magnitude of these in-gap states. Impedance spectroscopy shows that the enhanced charge transfer on the surface of the textured photoelectrodes is the origin for the catalytic efficiency of these devices.
This study hopes to pave the way towards a rational improvement in the electronic and catalytic properties of standalone undoped- BiVO4 as well as a new approach in designing highly efficient photoanodes for oxygen evolution.
[1] Abdi F.F., Savenije T.J., May M.M., Dan B., Krol R., J.Phys.Chem.Lett., 2013,4,2752-2757
[2] Park Y., McDonald K.J., Choi K.S., Chem.Soc. Rev., 2013,422321-2337.
[3] Shi X., Choi Y., Zhang K., Kwon J., Kim D.Y., Lee J., Ho L.S., Kim J.K., Park J.H., Nat. Comm., 5, 2014, 4775.
[4] Nair V.V., Perkins C.L., Law M., Submitted.

Figure 1
Engineering of Oxide Materials for Improved Photoelectrochemical Water Oxidation
Authors: Lin Yan-Gu , Hsu Yu-Kuei 
Published: February 2020

Global climate warming and environment pollution have spurred scientists to develop new high-efficient and environmental-friendly energy technologies. Hydrogen is an ideal fuel for fuel cell applications. Hydrogen has to be produced from renewable and carbon-free resources using nature energies such as sunlight if one thinks of clean energy and environmental issues. In this regard, a photoelectrochemical (PEC) cell consisting of semiconductor photoelectrodes that can harvest light and use this energy directly for splitting water is a more promising way for hydrogen generation. Abundant and inexpensive oxide semiconductor such as ZnO has been recognized as a promising photoelectrode, but the photoconversion efficiency is substantially limited by its large band gap and rapid charge recombination. Recently, doping with 4d transition metal, such as Mo, has been carried out to remarkably enhance the PEC performance of many photoanodes including TiO2, BiVO4, and Fe2O3. Nevertheless, 1-D Mo-doped ZnO nanostructures have not been reported for PEC water splitting. We report the first demonstration of cobalt phosphate (Co-Pi) assisted Zn1-xMoxO nanorods (NRs) as visible-light-sensitive photofunctional electrodes to fundamentally improve the performance of ZnO NRs for PEC water splitting. The maximum photoconversion efficiency could be successfully achieved as high as 1.05%, with the significant photocurrent density of 1.4 mA cm-2. More importantly, in addition to achieve the maximum incident photon to current conversion efficiency (IPCE) value of 86%, it could be noted that the IPCE of Zn1-xMoxO photoanodes at the monochromatic wavelength of 450 nm is up to 12%. Our PEC performances are comparable to those of many oxide-based photoanodes in recent reports. The improvement in photoactivity of PEC water splitting may be attributed to the enhanced visible-light absorption, increased charge-carrier densities, and improved interfacial charge-transfer kinetics due to the synergistic effects of Mo incorporation and Co-Pi modification, thus contributing to photocatalysis. The new design of constructing highly photoactive Co-Pi assisted Zn1-xMoxO photoanodes enriches the doping community and sheds light on developing high efficiency photoelectrodes for solar-hydrogen field.
Reference:
[1] Y.G. Lin, Y.K. Hsu, Y.C. Chen, S.B. Wang, J.T. Miller, L.C. Chen, and K.H. Chen, Energy Environ. Sci., 5, 8917 (2012).
[2] Y.G. Lin, Y.K. Hsu, Y.C. Chen, L.C. Chen, S.Y. Chen, and K.H. Chen, Nanoscale, 4,6515 (2012).
[3] Y.K. Hsu, Y.C. Chen, Y.G. Lin, L.C. Chen, and K.H. Chen, J. Mater. Chem., 22, 2733 (2012).
[4] Y.G. Lin, Y.K. Hsu, A.M. Basilio, Y.T. Chen, K.H. Chen, and L.C. Chen, Optics Express, 22, A21 (2014).
[5] Y.K. Hsu, S.Y. Fu, M.H. Chen, Y.C. Chen, and Y.G. Lin, Electrochimica Acta, 120, 1 (2014).
[6] Y.G. Lin, Y.C. Chen, J.T. Miller, L.C. Chen, K.H. Chen, and Y.K. Hsu, ChemCatChem, 6, 1684 (2014).
[7] Y.G. Lin, Y.K. Hsu, Y.C. Chen, B.W. Lee, J.S. Hwang, L.C. Chen, and K.H. Chen, ChemSusChem, 7, 2748 (2014).
Near-Isothermal Doped-Hercynite Redox Cycle for Solar-Thermal Water Splitting
Authors: Muhich Christopher , Ehrhart Brian , Alshankiti Ibraheam , Ward Barbara , Musgrave Charles , Weimer Alan 
Published: February 2020

Hydrogen productivity exceeding 350 micromoles H2/g total redox material has been demonstrated for near-isothermal processing using the doped-hercynite cycle for oxidation with steam carried out at 1350oC following 1500oC reduction. This temperature difference driving the redox is quite narrow compared to standard 500oC temperature swing (T-swing) redox processing. Such near-isothermal processing substantially reduces the difficult solid/solid heat recuperation, the energy required to heat back up to reduction temperatures following oxidation and the thermal stresses associated with heating/cooling active materials associated with standard T-swing redox cycling. Evidence is provided indicating that the cycle occurs via an oxygen-vacancy formation process. Efficiency analysis identifies isothermal processing with perfect steam/steam heat exchange as providing for the highest theoretically possible efficiency. Although it may be impossible to operate isothermally with perfect gas/gas heat exchange in practice, it does provide for an optimal “stretch” target to aim for. Near-isothermal operation seems achievable in practice and may provide for the most realistic efficient mode of operation.