The high CO tolerance of PtRu electrocatalysis, compared with pure Pt and other Pt-based alloys, makes it interesting as an anode material in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). This report describes the formation of bimetallic PtRu nanofilms using the electrochemical form of atomic layer deposition (E-ALD). Metal nanofilm formation using E-ALD is facilitated by use of surface-limited redox replacement (SLRR), where an atomic layer (AL) of a sacrificial metal is first formed by UPD. The AL is then spontaneously exchanged for a more noble metal at the open-circuit potential (OCP). In the present study, PtRu nanofilms were formed using SLRR for Pt and Ru, and Pb UPD was used to form the sacrificial layers. The PtRu E-ALD cycle consisted of Pb UPD at −0.19 V, followed by replacement using Pt(IV) ions at OCP, rinsing with blank, then Pb UPD at −0.19 V, followed by replacement using Ru(III) ions at OCP. PtRu nanofilm thickness was controlled by the number of times the cycle was repeated. PtRu nanofilms with atomic proportions of 70/30, 82/18, and 50/50 Pt/Ru were formed on Au on glass slides using related E-ALD cycles. The charge for Pb UPD and changes in the OCP during replacement were monitored during the deposition process. The PtRu films were then characterized by CO adsorption and electrooxidation to determine their overpotentials. The 50/50 PtRu nanofilms displayed the lowest CO electrooxidation overpotentials as well as the highest currents, compared with the other alloy compositions, pure Pt, and pure Ru. In addition, CO electrooxidation studies of the terminating AL on the 50/50 PtRu nanostructured alloy were investigated by deposition of one or two SLRR of Pt, Ru, or PtRu on top.

•CV of Au in Mo and Se precursor solutions were examined at different pH.•E-ALD cycle chemistry was developed to electrodeposit MoSe2 thin films.•Presence of MoSe2 in as-deposited films was confirmed by PEC measurements.•Thermal annealing led to an enrichment of MoSe2 in the deposits.•Se can be used to induce Mo deposition, concomitantly forming MoSe2.Cyclic voltammetry (CV) of Au in MoO3 and SeO2 solutions was studied under both basic and acidic conditions, as a precursor to development of E-ALD cycle chemistry for the electrodeposition of MoSe2. Those results indicated that acidic HMoO4- and SeO2 precursor solutions would be a better choice for the formation of MoSe2 using E-ALD. Photoelectrochemical (PEC) photovoltage measurements revealed an optical band gap of 1.1 eV for the as-deposited MoSe2 films. Some unreacted MoO2 was detected by the PEC measurements, as well, but were removed by thermal annealing. Some excess elemental Se was also removed during the anneal, and Raman spectroscopy indicated that the films' crystallinity was improved. Deposit quality was followed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron probe microanalysis (EPMA). Se appeared to suppress Mo oxidation and induce MoSe2 film growth in the E-ALD cycle.

Crystalline thin films of cuprous selenide (Cu2Se) were electrodeposited at room temperature from an aqueous solution containing elemental precursors for Cu and Se, using a potential pulse version of atomic layer deposition. Cyclic voltammetry was used to estimate Anodic and Cathodic cycle potentials for the formation of Cu2Se, which were then examined to systematically optimize the cycle. Electron probe microanalysis was used to follow the Cu/Se atomic ratios as a function of the cycle parameters, and X-ray diffraction was used to investigate deposit structure: polycrystalline orthorhombic Cu2Se, with some cubic. Film thicknesses, from spectroscopic ellipsometry, were shown to be proportional to the number of cycles performed (0.02 nm/cycle), and scanning electron microscopy suggested that the deposits were consistent with layer-by-layer growth as a function of the number of cycles.

Indium(III) selenide, In2Se3, thin films were electrodeposited at room temperature from an aqueous solution containing ionic precursors for both In and Se, using potential pulse atomic layer deposition (PP-ALD). Cyclic voltammetry was used to determine approximate cycle potentials, and anodic and cathodic potentials were systematically examined to optimize the potential pulse program for In2Se3. Electron probe microanalysis was used to follow the In:Se atomic ratio as a function of the cycle conditions, and annealing studies were performed on stoichiometric deposits. Film thickness was a function of both the anodic and cathodic potentials. The optimum growth rate was consistent with previous PP-ALD studies in which similar concentrations and pulse times were employed, 0.02 nm/cycle. The use of the potential pulse cycle for film growth resulted in surface-limited control over the deposit stoichiometry each cycle and thus a layer-by-layer growth process.

Pd nanofilms were grown using electrochemical atomic layer deposition (E-ALD) and used as a platform for investigations into changes in hydrogen absorption/desorption kinetics as a function of the coverage of Rh. Surface limited redox replacement (SLRR) reactions were used to form Pd atomic layers. That is, Pd atomic layers were grown on polycrystalline Au by first depositing a sacrificial Cu atomic layer using underpotential deposition (UPD), and then exchanging it for PdCl42− ions at open circuit potential (OCP). That cycle was then repeated 15 times to form one of the Pd nanofilms used in this study. Rh was deposited on the 15 cycle Pd films from a RhCl63− solution at constant potential or using an E-ALD procedure, similar to that employed to form the Pd nanofilms. Cyclic voltammetry (CV) of the Pd films modified with various coverages of Rh were compared with unmodified Pd nanofilms. The resulting CVs indicated that the presence of Rh enhanced the rates of hydrogen absorption and desorption into and out of the underlying Pd nanofilm. Rh overlayers formed at 0 V for 60 s produced the greatest kinetic enhancement. Two possible explanations for the observed behavior are proposed and discussed.

The high CO tolerance of PtRu electrocatalysis, compared with pure Pt and other Pt-based alloys, makes it interesting as an anode material in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). This report describes the formation of bimetallic PtRu nanofilms using the electrochemical form of atomic layer deposition (E-ALD). Metal nanofilm formation using E-ALD is facilitated by use of surface-limited redox replacement (SLRR), where an atomic layer (AL) of a sacrificial metal is first formed by UPD. The AL is then spontaneously exchanged for a more noble metal at the open-circuit potential (OCP). In the present study, PtRu nanofilms were formed using SLRR for Pt and Ru, and Pb UPD was used to form the sacrificial layers. The PtRu E-ALD cycle consisted of Pb UPD at −0.19 V, followed by replacement using Pt(IV) ions at OCP, rinsing with blank, then Pb UPD at −0.19 V, followed by replacement using Ru(III) ions at OCP. PtRu nanofilm thickness was controlled by the number of times the cycle was repeated. PtRu nanofilms with atomic proportions of 70/30, 82/18, and 50/50 Pt/Ru were formed on Au on glass slides using related E-ALD cycles. The charge for Pb UPD and changes in the OCP during replacement were monitored during the deposition process. The PtRu films were then characterized by CO adsorption and electrooxidation to determine their overpotentials. The 50/50 PtRu nanofilms displayed the lowest CO electrooxidation overpotentials as well as the highest currents, compared with the other alloy compositions, pure Pt, and pure Ru. In addition, CO electrooxidation studies of the terminating AL on the 50/50 PtRu nanostructured alloy were investigated by deposition of one or two SLRR of Pt, Ru, or PtRu on top.

Pd thin films were formed by electrochemical atomic layer deposition (E-ALD) using surface-limited redox replacement (SLRR) of Cu underpotential deposits (UPD) on polycrystalline Au substrates. An automated electrochemical flow deposition system was used to deposit Pd atomic layers using a sequence of steps referred to as a cycle. The initial step was Cu UPD, followed by its exchange for Pd ions at open circuit, and finishing with a blank rinse to complete the cycle. Deposits were formed with up to 75 cycles and displayed proportional deposit thicknesses. Previous reports by this group indicated excess Pd deposition at the flow cell ingress, from electron probe microanalysis (EPMA). Those results suggested that the SLRR mechanism did not involve direct transfer between a CuUPD atom and a Pd2+ ion that would take its position. Instead, it was proposed that electrons are transferred through the metallic surface to reduce Pd2+ ions near the surface where their activity is highest. It was proposed that if the cell was filled completely before a significant fraction of the CuUPD atoms had been oxidized then the deposit would be homogeneous. Previous work with EDTA indicated that the hypothesis had merit, but it proved to be very sensitive to the EDTA concentration. In the present study, chloride was used to complex Pd2+ ions, forming PdCl42–, to slow the exchange rate. Both complexing agents led to a decrease in the rate of replacement, producing more homogeneous films. Although the use of EDTA improved the homogeneity, it also decreased the deposit thickness by a factor of 3 compared to the thickness obtained via the use of chloride.

Pd nanofilms were grown on Au(111) using the electrochemical form of atomic layer deposition (E-ALD). Deposits were formed by repeated cycles of surface-limited redox replacement (SLRR). Each cycle produced an atomic layer of Pd, allowing the reproducible formation of Pd nanofilms, with thicknesses proportional to the number of cycles performed. Pd deposits were formed with up to 30 cycles, in the present study, and used as a platform for studies of hydrogen sorption/desorption as a function of thickness. The SLRR cycle involved the initial formation of an atomic layer of Cu by underpotential deposition, followed by its galvanic exchange with PdCl42– ions at open circuit. The first three cycles were studied using in situ electrochemical scanning tunneling microscopy (EC-STM), which showed a consistent morphology from cycle to cycle and the monatomic steps indicative of layer-by-layer growth. Cyclic voltammetry was used to study the hydrogen sorption/desorption properties as a function of thickness in 0.1 M H2SO4. The results indicated that the underlying Au structure greatly influenced hydrogen adsorption, as did film thickness for deposits formed with fewer than five cycles. No hydrogen absorption occurred for the thinnest films, although it increased linearly for thicker films, producing an average H/Pd molar ratio of 0.6. Electrochemical annealing was shown to improve surface order, producing CVs that strongly resembled those characteristic of bulk Pd(111).

The growth of stoichiometric CuInSe2 (CIS) on Au substrates using electrochemical atomic layer deposition (E-ALD) is reported here. Parameters for a ternary E-ALD cycle were investigated and included potentials, step sequence, solution compositions and timing. CIS was also grown by combining cycles for two binary compounds, InSe and Cu2Se, using a superlattice sequence. The formation, composition, and crystal structure of each are discussed. Stoichiometric CIS samples were formed using the superlattice sequence by performing 25 periods, each consisting of 3 cycles of InSe and 1 cycle of Cu2Se. The deposits were grown using 0.14, −0.7, and −0.65 V for Cu, In, and Se precursor solutions, respectively. XRD patterns displayed peaks consistent with the chalcopyrite phase of CIS, for the as-deposited samples, with the (112) reflection as the most prominent. AFM images of deposits suggested conformal deposition, when compared with corresponding image of the Au on glass substrate.

Atomic-scale control in the formation of Pd thin films is being developed using electrochemical atomic layer deposition (E-ALD) via surface limited redox replacement (SLRR). Pd has unique hydrogen storage properties. To study hydrogen storage capacity, hydrogen charging and discharging kinetics and its catalytic properties at the nanoscale will require films with well-defined thickness and structure. SLRR is the use of underpotential deposition (UPD) to form a sacrificial atomic layer of a less noble metal, such as Cu or Pb, and to exchange it at open circuit potential (OCP) for a more noble metal (Pd) via galvanic displacement. The deposits were grown using an automated electrochemical flow cell system which allowed sequential variation of solutions and potentials. Electron probe microanalysis (EPMA) revealed excess growth at the flow cell ingress, suggesting that the SLRR mechanism involved electron transfer from substrate to Pd2+ ions, rather than direct electron exchange from sacrificial metal atom(s) to Pd2+ ions. Ethylenediaminetetraacetic acid (EDTA) was used to slow the galvanic displacement by complexing the Pd2+, in an attempt to form more uniform Pd deposits. The resulting films were more homogeneous and displayed the expected Pd voltammetry in H2SO4. The charge for UPD remained constant from cycle to cycle, indicating no roughening of the surface. Ways of optimizing complexing agent properties, as well as the flow cell design and deposition parameters are discussed.