Three-Dimensional Array of TiN@Pt₃Cu Nanowires as an Efficient Porous Electrode for the Lithium–Oxygen Battery

Abstract

The nonaqueous lithium-oxygen battery is a promising candidate as a next-generation energy storage system because of its potentially high energy density (up to 2-3 kW kg), exceeding that of any other existing energy storage system for storing sustainable and clean energy to reduce greenhouse gas emissions and the consumption of nonrenewable fossil fuels. To achieve high round-trip efficiency and satisfactory cycling stability, the air electrode structure and the electrocatalysts play important roles. Here, a 3D array composed of one-dimensional TiN@PtCu nanowires was synthesized and employed as a whole porous air electrode in a lithium-oxygen battery. The TiN nanowire was primarily used as an air electrode frame and catalyst support to provide a high electronic conductivity network because of the high-orientation one-dimensional crystalline structure. Meanwhile, deposited icosahedral PtCu nanocrystals exhibit highly efficient catalytic activity owing to the abundant {111} active lattice facets and multiple twin boundaries. This porous air electrode comprises a one-dimensional TiN@PtCu nanowire array that demonstrates excellent energy conversion efficiency and rate performance in full discharge and charge modes. The discharge capacity is up to 4600 mAh g along with an 84% conversion efficiency at a current density of 0.2 mA cm, and when the current density increased to 0.8 mA cm, the discharge capacity is still greater than 3500 mAh g together with a nearly 70% efficiency. This designed array is a promising bifunctional porous air electrode for lithium-oxygen batteries, forming a continuous conductive and high catalytic activity network to facilitate rapid gas and electrolyte diffusion and catalytic reaction throughout the whole energy conversion process.

A Critical Review on Functionalization of Air‐Cathodes for Nonaqueous Li–O2 Batteries

“…Engineering a cathode with both chemical inertness and exceptional electrochemical performance remains a challenge. Cost‐effective alternatives such as transition metal compounds, including oxides, carbides, and nitrides, are all been considered as cathode material for the LOB, but they all suffer from low electrical conductivity …”

“…Air‐electrodes with a high surface area, superior electrical conductivity, and excellent chemical and electrochemical stability with an efficient bifunctional catalytic activity toward ORR and OER are highly desired for LOBs. To circumvent problems associated with carbonaceous‐based air‐electrodes, e.g., reactivity between carbon and electrolyte/Li 2 O 2 and the consequent formation of carbonates/formates and acetates, high interfacial resistance, and overpotential, carbon‐free electrodes have been introduced . Employing a non‐carbonaceous catalyst as air‐cathode with a hydrophilic microporous structure can not only facilitate oxygen diffusion with sufficient electrolyte wettability but also mitigate side reactions by lowering the charge overpotential and reducing electrolyte decomposition.…”

“…Alternatively, inexpensive metal oxides and bifunctional TMC have been researched extensively as possible cathode materials. However, low electrical conductivity and in some cases insufficient catalytic activity resonated in poor cycle performance and round‐trip efficiency, demanding a conductance support, such as MoO 2 on nickel or nickel foam, and a noble metal‐based catalyst . Low mass loading and insufficient surface area are considered their Achilles heel.…”

“…Free‐standing metal and metal oxides, directly grown on a metallic conductive substrate, can ensure a lower interfacial resistance and mitigate possible degradation reactions associated with polymer binders . Free‐standing electrodes may improve LOB reversibility by affecting the morphology of Li 2 O 2 (mostly, but not limited to, film‐like morphology) and crystallinity of Li 2 O 2 . As in the case of carbon, morphology dependency on current density was observed with quasi‐amorphous Li 2 O 2 discharge products at higher current density .…”

“…Yet, questionable electrochemical stability and problematic electrical conductivity distanced its practical use in LOBs . Although TiN can catalyze oxygen reduction and serve as an ORR catalyst in LOB, it cannot facilitate Li 2 O 2 oxidation. In the presence of Li 2 O 2 , oxygen evolution is often inhibited due to surface oxidation of TiN and drastic increase in charge transfer resistance .…”