Synthesis and electrochemical study of Pt-based nanoporous materials

One step electrochemical route to the fabrication of highly ordered array of cylindrical nano porous structure and its electrocatalytic performance toward efficient hydrogen evolution

An efficient and non-precious metal catalyst is a key factor for hydrogen evolution reaction (HER). Here we report that the fabrication of highly ordered porous arrays of Cu-Zn-Ni alloy has been carried out in a one-step electrochemical route at a constant apparent current density of -3 A·cm^-2. The optimum film composition and reactivity of the electrodes for catalytic hydrogen evolution reaction were analyzed by using different current densities, deposition time and bath concentration. For this purpose, onset potentials in linear sweep voltammograms (LSV) were compared. The structure and morphology of nanoporous Cu-Zn-Ni and Cu-Zn alloy were characterized by SEM and energy dispersive X-ray (EDS) analysis. The experimental results on the behavior of electrocatalytic activity of prepared alloys showed that the addition of nickel to the alloys improves of the electrocatalytic performance of the electrodes toward HER. In addition, enhancement of electrochemical activity toward hydrogen evolution can be attributed to the large electrochemical active surface area and porous structure of Cu-Zn-Ni alloy. In order to improvement of reaction kinetics, Tafel plots were derived from LSV voltammograms, and the exchange current densities for HER on synthesized electrodes (Cu-Zn and Cu-Zn-Ni alloys) were calculated about 3.2 × 10^-5 and 2.1 × 10^-3 mA·cm^-2, respectively.

On the pH Dependence of the Potential of Maximum Entropy of Ir(111) Electrodes

Studies over the entropy of components forming the electrode/electrolyte interface can give fundamental insights into the properties of electrified interphases. In particular, the potential where the entropy of formation of the double layer is maximal (potential of maximum entropy, PME) is an important parameter for the characterization of electrochemical systems. Indeed, this parameter determines the majority of electrode processes. In this work, we determine PMEs for Ir(111) electrodes. The latter currently play an important role to understand electrocatalysis for energy provision; and at the same time, iridium is one of the most stable metals against corrosion. For the experiments, we used a combination of the laser induced potential transient to determine the PME, and CO charge-displacement to determine the potentials of zero total charge, (E_PZTC). Both PME and E_PZTC were assessed for perchlorate solutions in the pH range from 1 to 4. Surprisingly, we found that those are located in the potential region where the adsorption of hydrogen and hydroxyl species takes place, respectively. The PMEs demonstrated a shift by ~30 mV per a pH unit (in the RHE scale). Connections between the PME and electrocatalytic properties of the electrode surface are discussed.

Synthesis of hollow PtAg alloy nanospheres with excellent electrocatalytic performances towards methanol and formic acid oxidations

Hollow PtAg alloy nanospheres were synthesized via galvanic replacement reaction between silver nanoparticles and K₂PtCl₄ at 60 °C.

Electrocatalysis and photoelectrochemistry based on functional nanomaterials

Catalysis plays a key role in chemical production, energy processing, air purification, water treatment, food processing, and the life sciences. Nanostructured materials with high surface areas and some unique properties have received widespread interest in electrocatalysis and photocatalysis. Recently, the author’s research team has designed and studied a variety of novel functional nanomaterials. This review article is derived from the author’s 2013 Canadian Catalysis Lectureship Award Lecture and focuses primarily on the electrocatalytic activities of platinum- and palladium-based nanomaterials and the development of TiO2-based nanostructured photocatalysts. Palladium possesses several exceptional properties that may enable promising applications in hydrogen detection, purification, and storage. The significant roles of palladium-based nanomaterials in facilitating the growth of a hydrogen economy are addressed. As platinum-based catalysts are vital to the development of fuel cells and sensors, the design of high-performance platinum-based electrocatalysts is highlighted. Additionally, TiO2 is considered to be one of the most promising photocatalysts due to its nontoxicity, high stability, and cost effectiveness. The modification of TiO2 nanomaterials to achieve visible light response is discussed as well. It is anticipated that the development of advanced functional nanostructured catalysts will further improve the efficiency and reduce the cost of electrochemical and photochemical processes, making them more attractive in addressing the pressing global energy and environmental issues.

Photoassisted enhancement of the electrocatalytic oxidation of formic acid on platinized TiO₂ nanotubes

A solvothermal method is used to deposit Pt nanoparticles on anodized TiO2 nanotubes (T_NT). Surface characterization using SEM, EDX, and XRD indicates the formation of polycrystalline TiO2 nanotubes of 110 ± 10 nm diameter with Pt nanoparticle islands. The application of the T_NT/Pt photoanode has been examined toward simultaneous electrooxidation and photo(electro)oxidation of formic acid (HCOOH). Upon UV-vis photoillumination, the T_NT/Pt photoelectrode generates a current density of 72 mA/cm(2), which is significantly higher (∼39-fold) than that of the T_NT electrode (1.85 mA/cm(2)). This boosting in the overall current is attributable to the enhanced oxidation of formic acid at the T_NT/Pt-electrolyte interface. Further, a series of cyclic voltammetric (CV) responses, of which each anodic scan is switched to photoillumination at a certain applied bias (i.e., 0.2 V, 0.4 V, etc.), is used to identify the role of T_NT/Pt as a promoter for the photoelectrooxidation of formic acid and understand a carbon monoxide (CO)-free pathway. Chronoamperometric (j/t) measurements demonstrate the evidence of an external bias dependent variation in the time lag during the current stabilization. An analysis of the CV plots and j/t profiles suggests the existence of both the charge-transfer controlled process and the diffusion-controlled process during formic acid photoelectrooxidation.

Interaction of carbon monoxide with small metal clusters: a DFT, electrochemical, and FTIR study

The adsorption of CO molecules onto small metal clusters was studied using density functional theory (DFT) calculations, and experimental electrochemical and attenuated total reflection-Fourier transform infrared spectroscopic (ATR-FTIR) techniques were used to examine CO adsorbed onto nanostructures of similar composition. The adsorption strengths and CO vibrational stretching frequencies were calculated and analyzed for clusters of the form M–CO for all of the period 4, 5, and 6 d-block transition metals. A direct link between the νCO and the population of d orbitals of the metal was observed. All possible binding sites for CO on clusters of the form Pd4–CO, Pd2Pt2–CO, and Pd2Au2–CO were determined and the corresponding adsorption energies and CO stretching frequencies were examined. Pure Pd and bimetallic PdPt and PdAu nanostructures were fabricated and used as catalysts for the adsorption and electrochemical oxidation of CO. The relative quantities of CO molecules adsorbed to surface of the catalysts decrease in the order of PdPt > Pd > PdAu, consistent with our DFT results. The location of νCO bands of CO adsorbed onto the nanostructured catalysts were determined by means of ATR-FTIR spectroscopy and were found to have values close to that predicted by DFT. This paper shows that DFT calculations on very small metal clusters Mn–CO (n ≤ 4) can be a simple but effective way of screening catalysts for their adsorbing properties.