Electrocatalytic ethanol oxidation reaction: recent progress, challenges, and future prospects

Discover Nano Review Electrocatalytic ethanol oxidation reaction: recent progress, challenges, and future prospects Jasvinder Kaur1 · Ram K. Gupta3,4 · Anuj Kumar2,4 Received: 27 March 2024 / Accepted: 16 July 2024 © The Author(s) 2024  OPEN Abstract Direct ethanol fuel cells (DEFCs) have been widely considered as a feasible power conversion technology for portable and mobile applications. The economic feasibility of DEFCs relies on two conditions: a notable reduction in the expensive nature of precious metal electrocatalysts and a simultaneous remarkable improvement in the anode’s long-term performance. Despite the considerable progress achieved in recent decades in Pt nanoengineering to reduce its loading in catalyst ink with enhanced mass activity, attempts to tackle these problems have yet to be successful. During the ethanol oxidation reaction (EOR) at the anode surface, Pt electrocatalysts lose their electrocatalytic activity rapidly due to poisoning by surface-adsorbed reaction intermediates like CO. This phenomenon leads to a significant loss in electrocatalytic performance within a relatively short time. This review provides an overview of the mechanistic approaches during the EOR of noble metal-based anode materials. Additionally, we emphasized the significance of many essential factors that govern the EOR activity of the electrode surface. Furthermore, we provided a comprehensive examination of the challenges and potential advancements in electrocatalytic EOR. Keywords Electrocatalysts · Pt-based catalysts · Ethanol oxidation reaction · Direct ethanol fuel cells 1 Introduction 1.1 Logical motivation Every day, more and more people are finding it harder and more difficult to satisfy their insatiable need for energy. Nonrenewable and eco-friendly fossil fuels are on trend to meet the world’s enormous energy demands. Nevertheless, a lingering problem for society today is the creation of a self-motivated energy supply to help globally reduce fossil fuel’s depletion as well as environmental [1] issues [2, 3]. Finding abundant non-traditional options to bridge the difference of energy demand and supply is the pressing responsibility of our current generation. In this context, H 2-O2 fuel cells (FCs) are emerging, eco-friendly, and silent power systems offering the direct conversion of latent chemical energy into electricity [4, 5]. When it comes to portable electronics and light-duty cars, to avoid the risk of flammable H 2 (as fuel) and its expensive storage, the direct ethanol fuel cell (DEFC) is a great choice. However, the use of these devices at a practical level is still limited due to the requirement of inexpensive and high-performing electrocatalysts to catalyze the anode process, the ethanol oxidation reaction (EOR [6]) [4]. * Jasvinder Kaur, ; * Anuj Kumar, | 1Department of Chemistry, School of Sciences, IFTM University, Moradabad, Uttar Pradesh 244102, India. 2Department of Chemistry, GLA University, Mathura 281406, India. 3Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA. 4National Institute of Material Advancement, Pittsburg, KS 66762, USA. Discover Nano (2024) 19:137 | https://doi.org/10.1186/s11671-024-04067-9 Vol.:(0123456789) Review Discover Nano (2024) 19:137 | https://doi.org/10.1186/s11671-024-04067-9 1.2 Catalysts for direct ethanol fuel cells A significant amount of research has been conducted on the improvement of electrocatalytic kinetics in EOR using platinum (Pt) or Pt-based nanomaterials, as well as Pt-based hybrid materials combined with other transition metal oxides such as F e2O3, TiO2, SnO2, MnO, C u2O, and ZnO [4]. Recent studies have focused on examining the electrooxidation of Cn alcohols (n > 1) using noble metals including Pt, Au, and Pd, as well as their alloys. The selection of these metals is based on their inherent stability and robust catalytic activity [7, 8]. Withing this framework, the extensive research on the electrooxidation of C2H5OH began half a century ago, including several ground-breaking investigations [9]. In the 1960s, Petry et al. [10] reported significant advancements in surface electrochemistry methods, which have since undergone continual improvement. The significant findings obtained encompass several aspects: (i) a phenomenological elucidation of the anodic polarization curve, including the estimation of Tafel parameters for C 2H5OH oxidation in alkaline electrolyte on Ni and Pt/C; (ii) the identification of the co-catalytic effect of Ru in relation to Pt for EOR; (iii) an exploration of the potential-dependent adsorption of C2H5OH and CH3COOH on Pt, along with an examination of the pathway mechanism; and (iv) the development of a mathematical model to elaborate the behavior of a flooded porous electrode [11–13]. Initially, the feasibility of using C H3OH, C2H5OH, and HCOOH as anodic fuels combined with oxygen or air gas diffusion cathodes was explored for energy production. Liquid electrolytes such as concentrated H2SO4, H3PO4, or KOH first facilitate ionic conductivity on the anode side. During the 1970s and 1980s, the primary focus of research was on investigating the electrooxidation reaction mechanism and identifying the surface adsorbed species that served as intermediates or catalytic poisons. However, advancements were obtained during this period with the advent of novel procedures for the fabrication of pristine single-crystal electrodes. Thus, Weaver et al. [14] performed a study to investigate the relative structural sensitivity of C2H5OH electrooxidation on single crystal Pt surfaces using Fourier-transform infrared spectroscopy (FT-IR) in combination with quasi-steady state voltammetry, exploring the fundamental findings of EOR intermediate adsorption on Pt surfaces. In their study, Stede et al. [15] fabricated an electrode composed of Pt alloyed with Mo, V, Cu, W, Mn, or Ce and supported on porous graphite as an anode. The electrode was subjected to direct C2H5OH oxidation in a solution containing 30 vol% C 2H5OH and 30 wt% H 2SO4 at 30 V, demonstrating excellent EOR performance of this alloyed electrode material. Although significant advancements have been achieved in the study of DEFCs, there are several unresolved inquiries pertaining to their efficiency and the underlying comprehension of their structural and mechanistic characteristics, as elaborated upon below [16]. 1.3 DEFCs’ shortcomings and potential remedies While there is a great deal of commercial potential for DEFCs, there are a number of obstacles to maximising their performance, including extremely sluggish EOR kinetics at the anode, partial oxidation of ethanol (C2H5OH), crossover of C 2H5OH [17], expensive noble metal catalysts, blocking of the catalyst’s active site due to sensitive EOR intermediates, less durability of the electrocatalyst, and water, as well as heat management [18]. Usually, the catalyst’s surface provides the active sites for the EOR process, reducin (...truncated)