Addressing the Global Energy Challenge with Fundamental Research

Global warming and climate change are terms that have become increasingly familiar to us in recent times. Many of our daily, usual activities contribute to these environmental challenges. Over the past century, human activity has significantly increased atmospheric levels of carbon dioxide (CO₂), nitrogen oxides, and sulfur oxides. Meanwhile, the rapid depletion of fossil fuels for industrial and technological development has led to irreversible environmental changes.

This alarming trend underscores the fact that natural carbon fixation, carried out by specialised microorganisms that can convert atmospheric CO2 into organic compounds, alone has become insufficient to counteract the effects of global warming. While there may not be a single solution to meet future energy demands and mitigate environmental consequences simultaneously, there is a growing urgency to take action. A deeper understanding of these challenges is essential, which is why fundamental scientific and technological research is at the core of the search for practical solutions.

Dr. Aryya Ghosh, Munmun Ghosh, and Deepak Asthana, Assistant Professors from the Department of Chemistry at Ashoka University, along with their research group, focus on contributing to this research by developing artificial energy sources while simultaneously reducing the excessive accumulation of greenhouse gases, particularly CO₂. Their efforts centre on converting CO₂ into value-added products, such as methane (CH₄), and producing hydrogen (H₂) from water or other proton sources, like acids. This could serve as a safer alternative fuel source to fossil fuels, as hydrogen generates only water as a byproduct. Electrocatalytic reduction of hydrogen ions (protons) (2H+ + 2e– → H2) is one of the readily available methods for producing hydrogen gas at large scales.

While there are multiple approaches to this field of study, this research is based on biomimetic molecular catalysis—a strategy inspired by nature’s efficiency in energy conversion. In nature, hydrogenase enzymes facilitate H₂ production by reducing protons. These enzymes, known as metalloenzymes, consist of iron or nickel coordinated with amino acids. Extensive studies have revealed how natural proton reduction occurs, yet we remain far from replicating nature’s extraordinary efficiency. This research study involves mimicking these enzymes and uncovering the mechanisms necessary to develop superior catalysts for hydrogen production. In this study, the research group has successfully synthesised a series of promising catalysts. Yet, one of the most significant challenges lies in understanding the precise reaction pathways that drive this catalytic activity.

The research work is the result of a collaborative effort between three research groups from the Chemistry Department at Ashoka University, each specialising in different areas of expertise. Dr. Munmun Ghosh’s research group focused on the electrocatalysis aspect, investigating catalysis via electrochemical methods, using catalysts synthesised by Dr. Deepak Asthana’s group. Meanwhile, Dr. Aryya Ghosh conducted a theoretical study of the reaction mechanism. Together, they combined their strengths to explore the catalytic activity of a well-known system for hydrogen generation. The researchers aimed to gain mechanistic insights into a well-known catalyst for the hydrogen evolution reaction (HER). The primary motivation of this collaboration being, to investigate the fundamental reaction mechanism.

“Our work sits at the intersection of chemistry, sustainability, and technological advancement. We believe it pushes the boundaries of possibility. Our main objective is not only to synthesise the best catalyst but also to study its mechanism thoroughly. This gives us enough opportunity to try for better catalysts and compare them with nature,” says Prof. Munmun Ghosh

Traditionally, HER catalysts operate via a metal-centred pathway that involves the formation of a metal-hydride intermediate. However, in the past decade, a new class of HER catalysts has emerged that follows an alternative ligand-centred route. To make the entire process more cost-effective, electrocatalysts derived from earth-abundant metals, such as Nickel (Ni), Zinc (Zn), and Iron (Fe), have gained attention. The researchers report the electrocatalytic activity of a series of pyridyl aroyl hydrazone (HL)-based metal complexes (ML₂, where M = Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn)) toward HER. The redox-active nature of the ligand and the presence of potential protonation sites facilitate ligand-centred reactivity in these complexes. Through a comprehensive mechanistic study of NiL₂ using both experimental and computational analyses, it was observed that all bond-forming and bond-breaking steps occur primarily at the ligand. In contrast, in the case of a metal-centred pathway, these steps take place at the metal centre.

The study hypothesised that the absence of a vacant site in the metal complex prevents the formation of a metal-hydride intermediate, thereby favouring a ligand-centred reaction pathway. A similar ligand-centred reactivity is anticipated for FeL₂, CoL₂, and CuL₂, although further confirmation is required.

Fundamental research truly does pave the way for groundbreaking innovation. Understanding the intricacies of hydrogen generation at a mechanistic level is the key to optimising and refining the process.

Prof. Munmun Ghosh also added – “By uncovering the precise reaction pathways and tuning catalytic properties, our work has the potential to drive significant advancements in sustainable energy.”

The ability to design materials with enhanced hydrogen production capabilities would be a significant leap forward in clean energy technology. The approach of combining experimental and computational insights places the research team from Ashoka University at the forefront of this effort.

Edited by Kangna Verma, Academic Communications, Research and Development Office

Reference Article:
Pyridyl Aroyl Hydrazone-Based Metal Complexes Showing a Ligand-Centered Metal-Assisted Pathway for Electrocatalytic Hydrogen Evolution
https://doi.org/10.1021/acsomega.4c07748
Authors: Dr. Munmun Ghosh, Dr. Aryya Ghosh, Dr. Deepak Asthana