Citation: Hasan, M.M. Environment-Friendly Ascorbic Acid Fuel Cell. Electrochem 2023, 4, 31–41. https://doi.org/10.3390/ electrochem4010003 Academic Editor: Masato Sone Received: 10 January 2023 Revised: 24 January 2023 Accepted: 28 January 2023 Published: 30 January 2023 Copyright: © 2023 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). electrochem Review Environment-Friendly Ascorbic Acid Fuel Cell Md. Mahmudul Hasan Research Organization for Nano and Life Innovation, Waseda University, Shinjuku, Tokyo 162-0041, Japan; hmahmudulche@gmail.com or hasan@aoni.waseda.jp Abstract: Recently, ascorbic acid (AA) has been studied as an environment-friendly fuel for energy conversion devices. This review article has deliberated an overview of ascorbic acid electrooxidation and diverse ion exchange types of AA-based fuel cells for the first time. Metal and carbon-based catalysts generated remarkable energy from environment-friendly AA fuel. The possibility of using AA in a direct liquid fuel cell (DLFC) without emitting any hazardous pollutants is discussed. AA fuel cells have been reviewed based on carbon nanomaterials, alloys/bimetallic nanoparticles, and precious and nonprecious metal nanoparticles. Finally, the obstacles and opportunities for using AA-based fuel cells in practical applications have also been incorporated. Keywords: ascorbic acid electrooxidation; electrocatalyst; PEM fuel cell; AEM fuel cell; split-pH fuel cell 1. Introduction The current energy system is predominately fossil-fuel-based and contributes to alarm- ing greenhouse emissions. This resulted in a greater need for alternative energy sources due to rising global energy demands driven by population increase and economic expansion. Modern wind and solar power technologies have developed quickly to provide sustainable and clean energy to meet energy demands. The geographical reliance, irregularity, and high starting costs of these energy generation methods put them at a competitive and economic disadvantage. Battery and fuel cell technologies that use renewable energy are receiving widespread attention in academia and business to overcome fossil fuel dependency [1]. In comparison to other sustainable energy sources, fuel cells are rapidly replacing gas, oil, coal, petroleum, etc. A fuel cell generates electricity from chemical energy and oxygen [2]. Direct liquid fuel cells (DLFCs) provide sustainable, carbon-neutral, and efficient power generation prospects. Transportation, permanent and mobile equipment, as well as a secondary power source are examples of DLFCs application [3]. The energy density of methanol is high, and it is also simple to store and distribute compared to hydrogen. Thus, a direct acidic methanol fuel cell (DMFC) is a preferable alternative for proton exchange membrane fuel cells (PEMFCs), where a cation exchange membrane (CEM) is used. The moderate toxicity of methanol and the catalyst poisoning (CO adsorption) that occurs in acidic DMFCs necessitate the use of expensive anode catalysts [4]. Direct formic acid fuel cells (DFAFCs) are gaining popularity because they have a lower fuel crossover and are less hazardous than methanol [3]. Conversely, it has less energy density and required costly Pt catalysts [3]. Furthermore, DFAFCs are highly vulnerable to CO poisoning on noble metals (Pt and Pd) during long-time operations [5]. Since ethanol is renewable and has a low level of toxicity, direct ethanol fuel cells (DEFCs) have been studied. However, even with precious metals, the ethanol oxidation rate is quite low in acidic environments [6]. Since the invention of anion exchange membranes (AEMs), many fuels can be oxidized efficiently in alkaline conditions compared to an acidic environment. In AEMs, hydroxyl ions are moved from cathode to anode over the membrane with lowered fuel crossover. In addition, the alkaline environment of AEM has benefits for water management, minimal Electrochem 2023, 4, 31–41. https://doi.org/10.3390/electrochem4010003 https://www.mdpi.com/journal/electrochem