Metallic Glasses are multi-component alloys with disordered atomic structures and unique and attractive properties such as ultra-high strength, soft magnetism, and excellent corrosion/wear resistance. In addition, they may be thermoplastically processed in the supercooled liquid region to desired shapes across multiple length-scales. Recently developed metallic glasses based on noble metals (such as Pt and Pd) are highly active in catalytic reactions such as hydrogen oxidation, oxygen reduction, and degradation of organic chemicals for environmental remediation. However, there is a limited understanding of the underlying electrochemical mechanisms and surface characteristics of catalytically active metallic glasses. Here, we demonstrate the influence of alloy chemistry and the associated electronic structure on the activity of a systematic series of Pt42.5−xPdxCu27Ni9.5P21 bulk metallic glasses (BMGs) with x = 0 to 42.5 at%. The activity and electrochemically active surface area as a function of composition are in the form of volcano plots, with a peak around an equal proportion of Pt and Pd. These amorphous alloys showed more than two times the hydrogen oxidation reactivity compared to pure Pt. This high activity was attributed to their lower electron work function and higher binding energy of Pt core level that reduced charge-transfer resistance and improved electrocatalytic activity from weakened chemisorption of protons.
To address the high cost associated with noble-metal-based amorphous catalysts, the performance of non-noble M100-xPx alloys was evaluated with a systematic variation in chemistry (M = Ni, Co; x = 0, 10, 15, 20, 30 at%). These alloys were synthesized by a scalable pulsed electrodeposition approach with glass formation seen in the range of 10 at% to 20 at% P. Enhanced corrosion resistance was observed with increasing phosphorus content as evidenced by the significant decrease in corrosion current density and ten-fold higher polarization resistance of M80P20 (M = Ni, Co) compared to its corresponding pure metal in representative electrolytes. Surface characterization showed enrichment of phosphorus in the passive layer, that likely promoted the restoration of the protective hypophosphite phase. The overpotential for hydrogen evolution reaction decreased by 35% and 45% in the case of Ni100−xPx and Co100−xPx, respectively, with increasing phosphorus content from 0 at% to 20 at%. Also, the M80P20 (M = Ni, Co) metallic glasses demonstrated excellent oxygen evolution reaction efficiency with a 10 mA/cm2 current density at 50% overpotential compared to pure Pt in alkaline media. The high activity and excellent durability of the non-noble amorphous alloys for hydrogen/oxygen evolution reactions (HER/OER) were attributed to the decreased binding energy of the P core level due to the synergy between the proton-acceptor (P centers) and hydride/hydroxide-acceptor (metal centers) sites.
| Identifer | oai:union.ndltd.org:unt.edu/info:ark/67531/metadc2178827 |
| Date | 07 1900 |
| Creators | Mahajan, Chaitanya |
| Contributors | Mukherjee, Sundeep, Reidy, Rick, Aouadi, Samir, Nasrazadani, Seifollah, Du, Jincheng |
| Publisher | University of North Texas |
| Source Sets | University of North Texas |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | Text |
| Rights | Public, Mahajan, Chaitanya, Copyright, Copyright is held by the author, unless otherwise noted. All rights Reserved. |
Page generated in 0.0017 seconds