energies Review A Comprehensive Review on the Recent Development of Ammonia as a Renewable Energy Carrier Muhammad Heikal Hasan 1,* , Teuku Meurah Indra Mahlia 1,* , M. Mofijur 1, I.M. Rizwanul Fattah 1 , Fitri Handayani 2, Hwai Chyuan Ong 1 and A. S. Silitonga 3 1 Centre for Green Technology, Faculty of Engineering and IT, University of Technology Sydney, Sydney, NSW 2007, Australia; MdMofi[email protected] (M.M.); [email protected] (I.M.R.F.); [email protected] (H.C.O.) 2 Department of Mechanical Engineering, Syiah Kuala University, Banda Aceh 23111, Indonesia; fi[email protected] 3 Department of Mechanical Engineering, Politeknik Negeri Medan, Medan 20155, Indonesia; [email protected] * Correspondence: [email protected] (M.H.H.); [email protected] (T.M.I.M.); Tel.: +61-4123-08541 (M.H.H.); +61-2951-490571 (T.M.I.M.) Abstract: Global energy sources are being transformed from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind, solar and hydrogen. The biggest challenge with hydrogen as a renewable energy carrier is the storage and delivery system’s complexity. There- fore, other media such as ammonia for indirect storage are now being considered. Research has shown that at reasonable pressures, ammonia is easily contained as a liquid. In this form, energy density is approximately half of that of gasoline and ten times more than batteries. Ammonia can provide effective storage of renewable energy through its existing storage and distribution network. Citation: Hasan, M.H.; Mahlia, In this article, we aimed to analyse the previous studies and the current research on the prepara- T.M.I.; Mofijur, M.; Rizwanul Fattah, tion of ammonia as a next-generation renewable energy carrier. The study focuses on technical I.M.; Handayani, F.; Ong, H.C.; advances emerging in ammonia synthesis technologies, such as photocatalysis, electrocatalysis and Silitonga, A.S. A Comprehensive plasmacatalysis. Ammonia is now also strongly regarded as fuel in the transport, industrial and Review on the Recent Development power sectors and is relatively more versatile in reducing CO2 emissions. Therefore, the utilisation of of Ammonia as a Renewable Energy ammonia as a renewable energy carrier plays a significant role in reducing GHG emissions. Finally, Carrier. Energies 2021, 14, 3732. https://doi.org/10.3390/en14133732 the simplicity of ammonia processing, transport and use makes it an appealing choice for the link between the development of renewable energy and demand. Academic Editor: Rob J.M. Bastiaans Keywords: ammonia; renewable energy storage; hydrogen storage Received: 30 April 2021 Accepted: 16 June 2021 Published: 22 June 2021 1. Introduction Publisher’s Note: MDPI stays neutral Industrial activity in parts of the world often has several direct and indirect adverse with regard to jurisdictional claims in environmental consequences. Carbon dioxide (CO2), a natural greenhouse gas (GHG) published maps and institutional affil- that helps keep the globe warm, is out of control and triggering a climate crisis. This iations. anthropogenic emission endangers human health, agriculture, natural ecosystems and atmospheric stability [1]. As reported in the Intergovernmental Panel on Climate Change (IPCC) Climate Change Mitigation Report (2014), CO2 is the main contributor to GHG emissions, which have 76% (including 11% of forests and land use) of the overall share, Copyright: © 2021 by the authors. while CH4 and N2O accounted for 16% and 6%, respectively [2]. According to National Licensee MDPI, Basel, Switzerland. Oceanic and Atmospheric Administration (NOAA), global ambient CO2 concentrations This article is an open access article rose from 280 ppm to 407.4 ppm in 2018, setting a new high for the last 800,000 years [3,4]. distributed under the terms and A growing number of international reports illustrates the health and environmental conditions of the Creative Commons effects of GHG emissions [5–7]. The ultimate goal is to maintain GHG concentrations Attribution (CC BY) license (https:// at a point where the dangerous effect of climate change can be prevented. In 1997, the creativecommons.org/licenses/by/ convention was supplemented and updated by the Kyoto Protocol [8]. Unlike the United 4.0/). Energies 2021, 14, 3732. https://doi.org/10.3390/en14133732 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 32 Energies 2021, 14, 3732 2 of 32 point where the dangerous effect of climate change can be prevented. In 1997, the conven- tion was supplemented and updated by the Kyoto Protocol [8]. Unlike the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol binds parties Nationsfrom a developed Framework country Convention to reduce on Climate GHG emissions Change (UNFCCC), [9]. Recently, the under Kyoto the Protocol terms bindsof the partiesParis Agreement from a developed of 2015, country the United to reduce Nations GHG (UN) emissions has committed [9]. Recently, itself under to a thelong-term terms oftarget the Paris to keep Agreement temperatures of 2015, below the United 2 °C, Nationscompared (UN) to haspre-industrial committed itselflevels, to to a long-termavoid the ◦ targetworst toconsequences keep temperatures of global below warming 2 C, [10,11]. compared Figure to 1 pre-industrial shows the top levels,10 countries to avoid on CO the2 worstemissions consequences worldwide of globaland their warming goal in [ 10the,11 Paris]. Figure Agreement.1 shows the top 10 countries on CO 2 emissionsIn the worldwide last decades, and the their world goal inhas the put Paris great Agreement. effort and investment into developing renewableIn the lastenergy decades, to decarbonise the world the has economy. put great The effort global and investmentpandemic disruption into developing caused renewableby COVID-19 energy teaches to decarbonise humanity thethat economy. reducing Thethe globalproportion pandemic of fossil disruption fuels in human caused byac- COVID-19tivity will teachessubstantially humanity increase that reducingthe regeneration the proportion of the Earth’s of fossil atmosphere fuels in human due activityto a re- willduction substantially in air pollution. increase For the example, regeneration in China, of the restricting Earth’s atmosphere the activity due of topeople a reduction caused inby air the pollution. COVID-19 For pandemic example, resulted in China, in a restricting 25% and 50% the activityreduction of in people CO2 and caused NO byX emis- the COVID-19sions, respectively pandemic [12,13]. resulted However, in a 25% theand problem 50% reductionwith these inrenewable CO2 and sources NOX emissions, of energy respectivelyis that they are [12 highly,13]. However, weather-dependent. the problem Therefore, with these it is renewable necessary sourcesto have an of affordable energy is thatand theyefficient are highlymethod weather-dependent. for storing energy. Several Therefore, prevailing it is necessary storage to technologies, have an affordable such as andchemical, efficient mechanical, method for electrical storing energy.and thermal Several energy prevailing storages, storage can be technologies, applied from such small as chemical,to large-scale mechanical, applications. electrical Prominent and thermal storage energy solutions, storages, such can as be batteries, applied provide from small dura- to large-scalebility and applications.technological Prominentsophistication storage but solutions,are far too such expensive as batteries, and cannot provide provide durability the andpower technological needed for sophisticationseasonal and grid-scale but are far demand. too expensive Consequently, and cannot hydrogen provide has the been power the needed for seasonal and grid-scale demand. Consequently, hydrogen has been the best best candidate since the 1970s, positioning this as both energy storage and a clean energy candidate since the 1970s, positioning this as both energy storage and a clean energy source [14]. However, storage and delivery issues associated with H2 remain an obstacle source [14]. However, storage and delivery issues associated with H2 remain an obstacle to its implementation [15]. To store and distribute H2 efficiently, other indirect storage to its implementation [15]. To store and distribute H2 efficiently, other indirect storage media such as ammonia (NH3), with its proven transportability and high flexibility, is media such as ammonia (NH ), with its proven transportability and high flexibility, is required [16]. 3 required [16]. Figure 1. Top 10 global CO2 emitters and the target in the Paris Agreement [17]. Figure 1. Top 10 global CO2 emitters and the target in the Paris Agreement [17]. InIn some some countries, countries, ammonia ammonia has has becomebecome a part of of their their energy energy roadmap. roadmap. For For exam- ex- ample,ple, Japan’s Japan’s Cross-Ministerial Cross-Ministerial Strategic Strategic Inno Innovationvation Program Program (SIP) (SIP) attempts attempts to show to show am- ammonia,monia, hydrides hydrides and and hydrogen hydrogen as as essential essential elements elements of the nation’snation’s hydrogenhydrogen energyenergy systemsystem [18 [18].]. The The Japanese Japanese Ministry Ministry ofof Economy,Economy, Trade Trade and and Industry Industry (METI) (METI) describeddescribed ammoniaammonia in in conjunction conjunction with with “the “the concept concept of of importing importing renewable renewable energy energy produced