## 1 Introduction  
Electrification has become one of the most-chosen paths to limit the air pollution derived from vehicles. As stated in [1, 2], electric and hybrid powertrains allow for a reduction in the environmental impact of vehicles on climate change and global warming. Recently, the increasing demand for more-efficient and less-polluting vehicles has also involved the sector of non-road mobile machinery (NRMM) [3, 4, 5, 6]. Among NRMM, agricultural tractors play an important role since they are a key element in the food supply chain. To reduce the impact of these vehicles and to be compliant with the increasingly stringent regulations, different strategies have been proposed, analysed and evaluated by studies available in the literature. Apart from electrification, alternative possible paths to follow are to adopt exhaust gas aftertreatment systems [7] or to use biofuels, such as biodiesel and biogas [8, 9], instead of traditional diesel. However, these strategies do not completely overcome the problem: the adoption of complex and bulky exhaust gas aftertreatment systems is often limited by the efficiency of the system and by on-board space availability, while the use of biofuels could led to an increase in emission levels of certain chemical species. Thus, other studies focused on the hybridization of tractor powertrains [10, 11, 12], which allows for downsizing of the thermal engine and show promising results in terms of fuel savings and efficiency improvements. However, these studies focused on hybrid architectures in which there is an internal combustion engine; therefore, the vehicle still produces harmful products deriving from the combustion process. In this context, fuel cell (FC) vehicles have gained a growing interest because they locally produce zero emissions and their refuelling time is comparable to that of a conventional powertrain with an internal combustion engine [13]. As a consequence, several studies have been carried out regarding the development and the analysis of fuel cell powertrains, including in passenger cars, light vehicles, trucks and off-road vehicles [14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. In particular, off-road vehicles and NRMM may require high operational time that, considering actual state-of-the-art battery technology, may not be compatible with pure battery electric vehicles due to high charging time and low endurance. On the contrary, fuel cell powertrains could be an alternative that at the same time meets the advantages of having no combustion processes, thus zero tank-to-wheel emissions, and high productivity [24]. However, to properly evaluate the environmental impact of fuel cell powertrains, the various hydrogen production methods should be taken into account using a life-cycle approach and exergy-based analysis [25; 26; 27], giving particular attention to innovative, less-pollutant and more-efficient processes [28; 29]. In order to avoid fast degradation, fuel cells alone cannot follow the almost instantaneous changes in power demands that are typical of a vehicular application; therefore, other on-board energy sources, such as batteries and ultra-capacitors, must be introduced [30; 31]. Thus, technological efforts are also being carried out to try to improve these additional on-board power sources that are necessary for the optimal operation of a fuel-cell-powered vehicle [32]. The introduction of one or more additional power sources leads to the necessary development of a proper energy management strategy (EMS) that determines the power split among the different sources [33; 34]. The development of the EMS is crucial for the optimal operation of the fuel cell hybrid power system [35; 36; 37]. With a view of analysing and optimizing the EMS of a hybrid fuel cell powertrain, the development of a scaled test bench for experimental measurements is an effective strategy. [PERSON] et al. [38] tested four hybrid fuel cell powertrain configurations with different batteries, supercapacitors and power converter combinations on a test bench.