J. Electrochem. Sci. Technol., 2024, 15(3), 321-344 - 321 - Elucidating Electrochemical Energy Storage Performance of Unary, Binary, and Ternary Transition Metal Phosphates and their Composites with Carbonaceous Materials for Supercapacitor Applications Muhammad Ramzan Abdul Karim 1 * ,† , Waseem Shehzad 1,† , Khurram Imran Khan 1 , Ehsan Ul Haq 2 *, and Yousaf Haroon 1 Faculty of Materials and Chemical Engineering, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology (GIKI), Topi- 23640, Khyber Pakhtunkhwa, Pakistan Department of Metallurgical and Materials Engineering, Faculty of Chemical, Metallurgical and Polymer Engineering, University of Engineering and Technology (UET), Lahore-54890, Pakistan ABSTRACT Transition metal compounds (TMCs) are being researched as promising electrode materials for electrochemical energy stor- age devices (supercapacitors). Among TMCs, transition metal phosphates (TMPs) have good, layered structures owing to open framework and protonic exchange capability among different layers, good surface area due to engrossed porosity, rich active redox reaction sites owing to octahedral structure and variable valance metallic ions. Hence TMPs become more ideal for supercapacitor electrode materials compared to other TMCs. However, TMPs have got some issues like low con- ductivity, rate performance, stability, energy, and power densities. But these problems can be addressed by making their composites with carbonaceous materials, e.g., carbon nanotubes (CNTs), graphene oxide (GO), graphitic carbon (GC), etc. A few factors like high surface area, excellent electrical conductivity of carbon materials and variable valence metal ions in TMPs caused great enhancement in their electrochemical performance. This article tries to discuss and compare the pub- lished data, majorly in last decade, regarding the electrochemical energy storage potential of pristine unary, binary, and ter- nary TMPs and their hybrid composites with carbonaceous materials (CNTs, GOs/rGOs, GC, etc.). The electrochemical performance of the hybrids has been reported to be higher than the pristine counterparts. It is hoped that the current review will open a new gateway to study and explore the high performance TMPs based supercapacitor materials. Keywords: Transition metal phosphates layered mesoporous structures, Carbonaceous materials, Supercapacitors, Energy storage Received : 1 January 2024, Accepted : 28 March 2024 1. Introduction With advancements in industry and commercial sector, there are many factors which create hindrance in their fast growth in which energy shortage is a seri- ous problem. There are many sources for energy pro- duction and used different pollution causing fuels like fossil fuels, biomass, and furnace oil. These energy resources produce electricity but mostly energy is not stored properly due to wastage of these fuels. This energy storage is very useful for small electronic instruments and electric vehicles (EV), Li- ion batteries (LIBs) [1,2]. LIBs have many limitations, i.e., risk for environment due to explosive nature of lith- ium and hazardous effects of fossil fuels. Among energy storage devices, supercapacitors performed better than classical LIBs and simple capacitors because of good combination of energy and power densities along with good capacity retention especially in case of asymmetric super capacitors (ASC). They are the combination of both pseudo capacitors (PD) (battery like properties) and electric double layer capacitors (EDLC) (capacitor like properties) [3–5] . Review Authors with equal contribution and sharing first authorship *E-mail address: MR Abdul Karim (ramzan.karim@giki.edu.pk / ramzan1109@hotmail.com) and EU Haq (amonehsan@uet.edu.pk) DOI: https://doi.org/10.33961/jecst.2024.00024 This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.