Water splitting has been widely considered to be an efficient way to generate sustainable and renewable energy resources in fuel cells, metal–air batteries and other energy conversion devices. Exploring efficient electrocatalysts to expedite the anodic oxygen evolution reaction (OER) is a crucial task that needs to be addressed in order to boost the practical application of water splitting. Intensive efforts have been devoted to develop mixed transition metal based chalcogenides as effective OER electrocatalysts. Herein, we have reported synthesis of a series of mixed metal selenides containing Co, Ni and Cu employing combinatorial electrodeposition, and systematically investigated how the transition metal doping affects the OER catalytic activity in alkaline medium. Energy dispersive spectroscopy (EDS) was performed to detect the elemental compositions and confirm the feasibility of compositional control of 66 metal selenide thin films. It was observed that the OER catalytic activity is sensitive to the concentration of Cu in the catalysts, and the catalyst activity tended to increase with increasing Cu concentration. However, increasing the Cu concentration beyond a certain limit led to decrease in catalytic efficiency, and copper selenide by itself, although catalytically active, showed higher onset potential and overpotential for OER compared to the ternary and quaternarymore »
(Invited Talk): Designing smart materials for efficient energy conversion: The story of transition metal chalcogenides
Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Among these, water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-air batteries, fuel cells, to solar-to-fuel energy conversion systems. In fact, solar water splitting is one of the most promising method to produce Hydrogen without depleting fossil-fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER), which is a kinetically sluggish, electron-intensive uphill reaction. A slow OER process also slows the other half- cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient OER electrocatalysts. We have proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal more »
- Award ID(s):
- 1710313
- Publication Date:
- NSF-PAR ID:
- 10064216
- Journal Name:
- 255th ACS National Meeting & Exposition, New Orleans, LA, United States, March 18-22, 2018 (2018), ENFL-330
- Sponsoring Org:
- National Science Foundation
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Designing efficient electrocatalysts has been one of the primary goals for water electrolysis, which is one of the most promising routes towards sustainable energy generation from renewable sources. In this article, we have tried to expand the family of transition metal chalcogenide based highly efficient OER electrocatalysts by investigating nickel telluride, Ni 3 Te 2 as a catalyst for the first time. Interestingly Ni 3 Te 2 electrodeposited on a GC electrode showed very low onset potential and overpotential at 10 mA cm −2 (180 mV), which is the lowest in the series of chalcogenides with similar stoichiometry, Ni 3 E 2 (E = S, Se, Te) as well as Ni-oxides. This observation falls in line with the hypothesis that increasing the covalency around the transition metal center enhances catalytic activity. Such a hypothesis has been previously validated in oxide-based electrocatalysts by creating anion vacancies. However, this is the first instance where this hypothesis has been convincingly validated in the chalcogenide series. The operational stability of the Ni 3 Te 2 electrocatalyst surface during the OER for an extended period of time in alkaline medium was confirmed through surface-sensitive analytical techniques such as XPS, as well as electrochemical methods whichmore »
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Transition metal selenides have attracted intensive interest as cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) because of the continuous thrust in sustainable energy conversion. In this article a Mn-based bifunctional electrocatalyst, MnSe, has been identified which shows efficient OER and ORR activity in alkaline medium. The catalytic activity could be further enhanced by using multiwalled carbon nanotubes (MWCNTs) which increases the charge transfer and electronic conductivity of the catalyst composite. This MnSe@MWCNT catalyst composite exhibits a very low overpotential of 290 mV at 10 mA cm −2 , which outperforms state-of-the-art RuO 2 as well as other oxide based electrocatalysts. Furthermore, the composite's facile OER kinetics was evidenced by its small Tafel slope of 54.76 mV dec −1 and low charge transfer resistance, indicating quick transport of the reactant species at the electrode interface. The MnSe@MWCNT also exhibited efficient electrocatalytic activity for ORR with an E onset of 0.94 V, which is among the best reported to date for chalcogenide based ORR electrocatalysts. More importantly, this MnSe-based ORR electrocatalyst exhibits high degree of methanol tolerance, showing no degradation of catalyst performance in the presence of copious quantities of methanol, thereby out-performing the state-of-the-art Ptmore »
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The two polymorphs of lithium cobalt oxide, LiCoO 2 , present an opportunity to contrast the structural requirements for reversible charge storage (battery function) vs. catalysis of water oxidation/oxygen evolution (OER; 2H 2 O → O 2 + 4H + + 4e − ). Previously, we reported high OER electrocatalytic activity from nanocrystals of the cubic phase vs. poor activity from the layered phase – the archetypal lithium-ion battery cathode. Here we apply transmission electron microscopy, electron diffraction, voltammetry and elemental analysis under OER electrolysis conditions to show that labile Li + ions partially deintercalate from layered LiCoO 2 , initiating structural reorganization to the cubic spinel LiCo 2 O 4 , in parallel with formation of a more active catalytic phase. Comparison of cubic LiCoO 2 (50 nm) to iridium (5 nm) nanoparticles for OER catalysis (commercial benchmark for membrane-based systems) in basic and neutral electrolyte reveals excellent performance in terms of Tafel slope (48 mV dec −1 ), overpotential ( η = ∼420 mV@10 mA cm −2 at pH = 14), faradaic yield (100%) and OER stability (no loss in 14 hours). The inherent OER activity of cubic LiCoO 2 and spinel LiCo 2 O 4 is attributedmore »
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Solar water splitting using photoelectrochemical cells (PEC's) is a promising pathway toward clean and sustainable storage of renewable energy. Practical realization of solar-driven synthesis of hydrogen and oxygen integrating light absorption and electrolysis of water has been challenging because of (1) the limited stability of good photovoltaic materials under the required electrochemical conditions, and (2) photovoltaic efficiency losses due to light absorption by catalysts, the electrolyte, and generated bubbles, or reflection at their various interfaces. Herein, we evaluate a novel integrated solar water splitting architecture using efficient silicon heterojunction photovoltaic cells that avoids such losses and exhibits a solar-to-hydrogen (STH) efficiency in excess of 10%. Series-connected silicon Heterojunction with Intrinsic Thin layer (HIT) cells generate sufficient photovoltage for unassisted water splitting, with one of the cells acting as the photocathode. Platinum is deposited on the back (dark) junction of this HIT cell as the catalyst for the hydrogen evolution reaction (HER). The photocathode is protected from corrosion by a TiO 2 layer deposited by atomic layer deposition (ALD) interposed between the HIT cell and the Pt, enabling stable operation for >120 hours. Combined with oxygen evolution reaction (OER) catalysts deposited on a porous metal dark anode, these PEC's achieve stablemore »
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