Synthesis of Multi-Metallic Alloy Nanoparticles and Electrochemical Applications on CO2 Conversion and Hydrogen Evolution Reaction
Authors: Kim Chansol , Song Ji-Yoon , Yoon Jeesoo , Jung Hee-Tae 
Published: August 2024

In this comprehensive research endeavor, we introduce two groundbreaking methodologies poised to reshape the landscape of nanocomposite material synthesis, unlocking unprecedented potential across a spectrum of electrochemical applications. The Joule heating method, also known as Carbothermal Shock (CTS), emerges as a remarkably simple yet highly effective technique for generating multi-metallic nanoparticles (NPs), including high-entropy alloys (HEA). The CTS process involves loading a metal precursor onto a carbon substrate and swiftly elevating the temperature through the passage of an electric current, inducing rapid thermal shock and resulting in the formation of small and uniform NPs. While the CTS method has showcased high performance in various applications, such as rechargeable energy storage systems and catalytic conversion, challenges persist in achieving optimal surface coverage of NPs, particularly for electrochemical applications. For example, metal NPs formed through the CTS method have not been used for electrocatalytic carbon dioxide (CO2) or nitrogen (N2) reduction reactions because the hydrogen evolution reaction (HER) and unwanted reactions occur on the exposed carbon substrate as a competing reaction

To overcome this challenge, we present a pioneering approach involving the utilization of partially carbonized cellulose as a novel carbon substrate. The cellulose matrix, distinguished by its unique structural characteristics, including interconnected aromatic rings and numerous edge sites, facilitates an unprecedented high surface coverage of various single and copper (Cu)-based polyelemental alloy NPs. The controlled manipulation of defect sites, such as vacancies and dangling bonds, within the carbonized cellulose plays a pivotal role in the nucleation and stabilization of metal NPs during the CTS process. The study underscores the correlation between defect sites on the carbon substrate and the resulting surface morphology of metal NPs, providing valuable insights for future advancements in nanocomposite material synthesis through the CTS method.

Moreover, the cellulose-enabled high surface coverage Cu NPs exhibit remarkable potential in electrocatalytic carbon dioxide (CO2) reduction reactions. The Cu NPs on cellulose/carbon paper (Cu/cellulose/CP) demonstrated a high ethylene selectivity of 48.92% at a potential of −0.529 V versus the reverse hydrogen electrode (RHE), maintaining stability over 30 hours of reaction in a 10 M KOH electrolyte. This study presents an exciting prospect for expanding the applications of polyelemental alloy NPs synthesized via the CTS method in diverse electrochemical applications.

Transitioning to the second part of the research, we explore the application of MXenes, a recently discovered family of two-dimensional materials composed of transition metal carbides and carbonitrides. These atomically thin layers exhibit a unique combination of metallic conductivity and high surface area due to their layered structure. To enhance the properties of MXenes and broaden their applications, various components, including organic small molecules, polymers, metals, and semiconducting materials, have been incorporated into their intrinsic nanostructures.

However, existing methods for fabricating MXene composite hybrid materials predominantly rely on solution processing techniques, introducing challenges such as severe MXene oxidation and nanoparticle aggregation. Addressing these limitations, we introduce a revolutionary rapid Joule heating approach, a solution-free method designed to synthesize a diverse range of MXene hybrid nanocomposites. This approach minimizes MXene oxidation on the surface and ensures a uniform distribution of nanoparticles on MXene surfaces without the drawbacks of severe aggregations. It became possible to synthesize metal NPs from unary to senary combinations (including Pt, Co, Ni, Fe, Cu components) with minimal MXene oxidation through rapid heating. The ability to easily modify the precursor ratio and synthesize unlimited combinations of MXene composite hybrid nanostructures enables the modulation of material properties to achieve high performance in diverse electrochemical applications. The resulting Pt-MXene hybrid nanostructure, synthesized through this novel approach, exhibits promising electrocatalytic performance for the hydrogen evolution reaction (HER) by minimizing MXene oxidation during the synthesis process. This breakthrough method holds immense potential for a wide range of catalytic applications, where the synergistic effects of MXene composites can significantly contribute.