Hydrogen Sorption Kinetics on Bare and Platinum-Modified Palladium Nanofilms, Grown by Electrochemical Atomic Layer Deposition (E-ALD)

Abstract

Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd. Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H2SO4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.

Enhanced Kinetics of Electrochemical Hydrogen Uptake and Release by Palladium Powders Modified by Electrochemical Atomic Layer Deposition

“…Studies of E-ALD have, thus far, primarily involved deposition on flat surfaces, ,− except for studies using SLRR, which was initially developed to coat the surfaces of nanoparticles with minimum quantities of catalytic metals. , The present study was undertaken to investigate similar deposits on the surfaces of three-dimensional materials in the form of submicron-sized powders. Such powders have applications in hydrogen separation, fuel cells, sensors, and catalysts. − Prior work on hydrogen reactions with powders has involved both elemental and alloy powders. − Powders typically allow for a much larger electrochemical surface area, for a given superficial surface area, compared with a planar substrate, increasing the rates of interfacial reactions .…”

“…SLRR on nanoparticles was previously demonstrated by Pt deposition on Au nanoparticles for oxygen reduction. 18 Previous work has shown that modification of the surface of a Pd nanofilm with Rh 19 or Pt 20,21 using E-ALD resulted in enhanced rates for H absorption and desorption. This is expected because of a less stable surface hydride on Rh or Pt, as compared with Pd.…”

Recent advances of doping strategy for boosting the electrocatalytic performance of two-dimensional noble metal nanosheets

“…In study of Zhao, High-quality, ultrathin (∼2.2 nm) 2D PdSe 2 flakes are achieved on mica substrates through a NaCl-assisted ambientpressure CVD [133]. Stickney grew nanofilms of Pd using an electrochemical form of ALD (E-ALD) on 100 nm evaporated Au films on glass [134]. Jacques Rozière discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode [135].…”

Ultrathin Film PtxPd(1-x) Alloy Catalysts for Formic Acid Oxidation Synthesized by Surface Limited Redox Replacement of Underpotentially Deposited H Monolayer

“…Another supporting factor is that Pt has a higher work function compared to Pd [109]. Finally, the extra Pt in the deposit could also be due to the slightly faster displacement kinetics between Pt and H atoms as compared to that of the competing Pd counterpart [110,111]. The analysis of all XPS composition characterization results suggest that the solution composition ratio between Pt and Pd chloride complexes could still be used for relatively accurate control of the Pt:Pd ratio in large compositional range of alloy films deposited by SLRR of H upd .…”