Contents lists available at ScienceDirect Molecular Catalysis journal homepage: www.elsevier.com/locate/mcat Review An inclusive review on the synthesis of molybdenum carbide and its hybrids as catalyst for electrochemical water splitting Osama Rabi, Erum Pervaiz*, Rubab Zahra, Maryum Ali, M. Bilal Khan Niazi Department of Chemical Engineering, School of Chemical and Materials Engineering (SCME), National University of Sciences & Technology (NUST), Sector H-12, Islamabad, 44000, Pakistan ARTICLE INFO Keywords: Molybdenum carbide Electrocatalysts Hydrogen evolution reaction Water splitting Oxygen reduction reaction ABSTRACT The world is using lot of fossil fuels due to increase in energy demand. This results in high production of CO 2 which is the main reason for global warming and harmful for the environment. These issues have driven the scientists to develop environment friendly alternative energies to replace these harmful fuels. Hydrogen has become one of the most promising fuels which are environment friendly and sustainable. To produce this green and clean source of energy, electrochemical water splitting has become one of the most suitable routes. For the efficient hydrogen evolution reaction (HER) an active catalyst is required to achieve high conversion efficiency. Many catalysts have been reported in the literature for hydrogen production through different methods. But Molybdenum carbide (Mo 2 C) has attracted a lot of attention and attraction to produce hydrogen through HER due to its high surface activity and electrochemical properties. In this review, the recent research progress has been reported on the Mo 2 C for HER mechanism. Different methods for the synthesis of Mo 2 C and its hybrid has been discussed extensively, along with different strategies to modify the physicochemical properties of Mo 2 C and its hybrid. Furthermore, the application of Mo 2 C related to its activity, durability, activation, and deactivation mechanism of the catalyst are critically reviewed. It is concluded that by the addition of another component in Mo 2 C can enhance the activity of the catalyst and gives more conversion rate. Hence, it realizes that Mo 2 C certainly can be used as an alternative catalyst for hydrogen production via water splitting. 1. Introduction 1.1. Why the need of renewable source of energy In the past few decades, the consumption of fossil fuels increased due to increase in the demand for energy. This created many environmental issues resulting in increased interest in the research and development of alternative renewable energy sources [1–3]. Due to utilization of the fossil fuels, carbon dioxide is produced which is considered as the main contributor to the greenhouse gas effect and climate changes. In the recent decades, intense industrial revolution and increase in world’s population have led to the rapid consumption of https://doi.org/10.1016/j.mcat.2020.111116 Received 31 May 2020; Received in revised form 30 June 2020; Accepted 6 July 2020 Abbreviations: Mo 2 C, molybdenum carbide; HER, hydrogen evolution reaction; OER, oxygen evolution reaction; CO 2 , carbon dioxide; H 2 S, hydrogen sulfide; PEM, proton exchange membrane; Pt, platinum; Pd, palladium; IrO 2 , iridium dioxide; RuO 2 , ruthenium oxide; CdS, cadmium sulfide; ZnCdS, zinc cadmium sulfide; C 3 N 4 , carbon nitride; MoS 2 , molybdenum disulfide; G, grams; mL, milliliters; DI water, deionized water; SiO 2 , silicon dioxide; NH 3 ⋅H 2 O, ammonium hydroxide; HF, hydrogen fluoride; HCl, hydrochloric acid; Pa, pascal; Mo, molybdenum; h, hours; H, hydrogen; KOH, potassium hydroxide; M, molar; AHM, ammonium hepta- molybdate; Co-NC@Mo 2 C, cobalt-nitrogen doped carbon@molybdenum carbide; NC@Mo 2 C, nitrogen doped carbon @ molybdenum carbide; N-CNTs/Ni, nickle/ nitrogen doped carbon nanotube; Ni(NO 3 ) 2 ⋅6H 2 O, nickle nitrate hexahydrate; Na 2 MoO 4 , sodium molybdate; CoCl 2 , cobalt chloride; SrTiO 3 , strontium titanate; CNT- SC, carbon nanotubes-single layer carbon atom; MF, melamine-formaldehyde; PVA, polyvinyl alcohol; PDDA, poly (diallyldimethylammonium chloride); GF, gra- phite felt; Mo 2 C@NC, molybdenum carbide@ nitrogen doped carbon; Ar, argon; MgO, magnesium oxide; D201, anion exchange resin; NaCl, sodium chloride; KCl, potassium chloride; Mo 2 (CN), molybdenum carbide doped carbon nanosheets; GLC, glucose; rGO, reduced graphene oxide; AM, ammonium molybdate; CH 4 , me- thane; TiO 2 , tin dioxide; WC, tungsten carbide; Al 2 O 3 , aluminium oxide; MoO 2 , molybdenum oxide; Pd(NH 3 ) 4 (NO 3 ) 2 , tetraamminepalladium (II) dinitrate; H 2 PtCl 6 , hexachloroplatinic acid; Cu(NO 3 ) 2 , copper nitrate; CuCl 2 , copper chloride; Co(NO 3 ) 2 , cobalt nitrate; FeCl 2 , iron chloride; PEG, polyethylene glycol; PVP, poly- vinylpyrrolidone; CTAB, cetyltrimethylammonium bromide; SDBS, sodium dodecylbenzenesulfonate; MoO 3 , molybdenum trioxide; AC, actinium; K 2 CO 3 , potassium carbonate; C dl , double layered capacitance; EIS, electrochemical impedance spectroscopy; CV, cyclic voltammetry; ECSA, electrochemical active surface area; LSV, linear sweep voltammetry; AC, activated carbon ⁎ Corresponding author. E-mail address: erum.pervaiz@scme.nust.edu.pk (E. Pervaiz). Molecular Catalysis 494 (2020) 111116 2468-8231/ © 2020 Elsevier B.V. All rights reserved. T