Turning Indium Oxide into a Superior Electrocatalyst: Deterministic Heteroatoms

Abstract

The efficient electrocatalysts for many heterogeneous catalytic processes in energy conversion and storage systems must possess necessary surface active sites. Here we identify, from X-ray photoelectron spectroscopy and density functional theory calculations, that controlling charge density redistribution via the atomic-scale incorporation of heteroatoms is paramount to import surface active sites. We engineer the deterministic nitrogen atoms inserting the bulk material to preferentially expose active sites to turn the inactive material into a sufficient electrocatalyst. The excellent electrocatalytic activity of N-In 2 O 3 nanocrystals leads to higher performance of dye-sensitized solar cells (DSCs) than the DSCs fabricated with Pt. The successful strategy provides the rational design of transforming abundant materials into high-efficient electrocatalysts. More importantly, the exciting discovery of turning the commonly used transparent conductive oxide (TCO) in DSCs into counter electrode material means that except for decreasing the cost, the device structure and processing techniques of DSCs can be simplified in future. Increasing energy demands have stimulated intense research on electrocatalysts for oxygen reduction reaction, water reduction reaction and triiodide (I 3 2 ) reduction reaction etc, which are at the heart of the typical key renewable-energy technologies such as fuel cells 1,2 , water splitting 3,4 , dye-sensitized solar cells (DSCs) 5,6 and so on. Platinum (Pt) is always the suitable electrocatalyst for these reduction reactions due to its high conductivity, good catalytic activity and chemical stability, but its low abundance ratio and high costs precluded the large-scale utilizations of these renewable-energy technologies. These considerations have led to ongoing efforts to design molecular catalysts that employ earth-abundant materials, to match up to or surpass the catalytic activity of Pt. Because high electric conductivity and good catalytic activity are the two main requirements for an efficient electrocatalyst, screening the alternatives among the abundant conductive materials like conductive oxides is a reasonable way. However, according to our previous theoretical research 7 , some conductive oxides such as indium oxide (In 2 O 3 ), stannic oxide (SnO 2 ) and zinc oxide (ZnO) are unfortunately proven to be electrocatalytically inactive, due to their low adsorption energies of reactant molecules and scarce active sites which are necessary for adsorption of the reactants, bond-breaking and bond-formation, and desorption of the products in the heterogeneous catalytic process 8 . To deliver these intrinsically inactive but abundant materials into active catalysts, one needs to control the atomic-scale surface structure to preferentially expose a greater fraction of the active sites 9 or exhibit a higher adsorption energy, which is highly challenging but desirable. Along the way, recent studies have shown that doping the carbon nanotubes and graphene with heteroatoms or defects sites can...

The search for efficient electrocatalysts as counter electrode materials for dye-sensitized solar cells: mechanistic study, material screening and experimental validation

“…26 To enable these materials to be active for the triiodide reduction reaction, N atoms were purposely incorporated into the In 2 O 3 nanocrystals. As depicted in Figure 14 60 Clearly, the E I ad value of In 2 O 3 after N doping is well within the optimal range for a good electrocatalyst, indicating an increased catalytic activity. This theoretically affirmative result encouraged the use of N-In 2 O 3 as a CE material in DSCs.…”

“…This theoretically affirmative result encouraged the use of N-In 2 O 3 as a CE material in DSCs. 60 Compared with the undoped In 2 O 3 counterpart, N-In 2 O 3 exhibited remarkable electrocatalytic activity, resulting in a PCE as high as 7.78%, which is higher than that of the DSCs equipped with the Pt CE (Figure 14).…”

Theory and applications of surface micro‐kinetics in the rational design of catalysts using density functional theory calculations

“…In addition, under the guidance of activity window for IRR, we successfully modified In 2 O 3 , initially an inert material for CE in DSSC, into a superior electrocatalyst by doping N heteroatoms. DFT calculations indicated that of CH 3 CN/N‐In 2 O 3 () is significantly enhanced compared to pure In 2 O 3 () which is originally outside of the ‘good IRR catalysts'region . Experiments confirmed that N‐modified In 2 O 3 do hold much higher IRR activity than its N‐free counterpart.…”

Improved catalytic activity of Pt/rGO counter electrode in In2O3-based DSSC

“…Zhang et al mentioned that In 2 O 3 with higher mobility reduces the charge transport and increases the catalytic activity for I 3 − reduction of Pt [34]. Commonly, Pt is used as the CE in In 2 O 3 -based DSSCs [35,36].…”