## 2 Research Method
### Literature Reviews and Key Findings
A simulation-based life cycle assessment (LCA) compared the environmental and health impacts of several glycerol-based hydrogen production technologies--ATR, APR, and SCWR--versus those of the conventional method of SMR [17; 18]. A techno-economic analysis (TEA) compared the cost of hydrogen produced from APR and steam reforming of glycerol, revealing that APR is slightly less expensive but still not competitive with SMR [18]. Another report on pathways to producing H\({}_{2}\) from biomass provided H\({}_{2}\) production costs and TRLs of SCWR, APR, and SR of glycerol [16]. Water electrolysis is widely considered a promising method of sustainably producing H\({}_{2}\) due to fairly negligent carbon emissions [19; 20; 21]. A number of sources compared powering electrolyzers with the local electricity grid mix versus renewables. Because the grid mix varies so widely, a wide range of H\({}_{2}\) cost values were reported, but in general, it is agreed that costs could be reduced by strategically utilizing renewable power sources rather than relying on the grid mix [22; 23; 24; 25; 26]. Research has recently explored utilizing wind power and solar PV power to produce green H\({}_{2}\) by electrolysis [20]. While discussed to a lesser extent, other renewables like hydropower and nuclear power are also contenders for more sustainable electrolysis power sources [27; 28; 29]. While hydropower is a well-established renewable electricity source, one report noted that it will be overtaken by solar PV power due to its lower levelized cost of electricity (LCOE) and higher energy capacity [30]. Nuclear energy is also a firmly established renewable energy source, but still, setbacks such as social apprehension keep it from becoming the focus of green H\({}_{2}\) research [28]. Different renewable energy sources make more sense for different areas, depending on which natural resources are most abundant and consistent in a given region [25]. Therefore, cost and energy efficiency analyses [31] are further complicated with the additional variable of energy source. The TRL of water electrolysis varies depending on the technology and the energy source utilized. However, as explored in a variety of reports, electrolysis is a fairly well-developed technology, particularly AKE, PEM, and SOE--more so than AEM [9; 16; 22; 32; 33; 34; 35]. In addition to its nearly negligible global warming impact, its high TRL makes electrolysis an attractive green H\({}_{2}\) production technology. However, high H\({}_{2}\) production costs and high energy require ments are setbacks that are keeping electrolysis from replacing the conventional methods. One paper noted that despite its low GWP and high technological readiness, solar PV-powered electrolysis will only be able to take the forefront as a potential option for H\({}_{2}\) production when its energy efficiency is improved, which will also subsequently lower its high production costs [5; 36]. Electrolyzers are oftentimes divided into two classes: low-temperature electrolyzers (LTEs) and high-temperature electrolyzers (HTEs). The U.S. DOE has invested R&D funding into these two types of electrolysis in order to promote the most durable, effective, and efficient system of green H\({}_{2}\) production. The characteristics of LTE, such as PEM, is that it is commercially available, but it is not durable, efficient, or affordable enough, while the characteristics of HTE, such as SOE, are that it is less mature but has potential for higher efficiency and a longer lifespan [37]. According to one paper, SOEs are advantageous because of their ability to co-electrolyte steam and carbon dioxide in a single step and, thus, eliminate the need for expensive and maintenance-intensive water-gas shift reactors [38]. SOEs operate at high temperatures, meaning that they require greater energy input, but also that they can utilize low-cost active metals rather than expensive noble metals [38].