ABSTRACT This study evaluates the feasibility of a hybrid hydrogen fuel cell–battery power supply for lower limb assistive exoskeletons. The objective is to determine whether this architecture can provide a realistic alternative to conventional lithium‐ion batteries in terms of autonomy, mass, and responsiveness to dynamic loads. Starting from a gait‐cycle power profile, the electrical demand of a six‐joint exoskeleton is estimated for a reference scenario of 10 000 assisted steps per day, corresponding to approximately 170 Wh. A battery‐only configuration and a hybrid fuel cell–battery system are then sized and compared at first‐order system‐level. The results indicate that, under the current technological assumptions, the hybrid configuration is heavier than the battery‐only solution while providing a lower driving range, demonstrating that it offers no practical advantage. A sensitivity analysis identifies gravimetric hydrogen storage capacity as the dominant parameter affecting system performance, whereas improvements in fuel cell stack specific power have a more limited effect. Increasing the storage capacity of the selected metal‐hydride system from 1.5 to 3 wt% would substantially reduce total mass and increase specific energy, making hybrid architectures more competitive for wearable robotics.
ABSTRACT This article focuses on two distinct methods for manufacturing an innovative solid oxide electrolysis cell and enhancing its electrochemical performances. On the hydrogen side, the support porosity was increased and optimized to prevent gas diffusion limitations at high current densities. To quantify the porosity rate, two experimental techniques were compared: image analysis and mercury intrusion porosimetry (MIP). On the oxygen side, a new material and deposition technique were employed with the aim of obtaining nanostructured electrodes. All of these developments were integrated into a complete cell, and electrochemical performances (in both solid oxide electrolysis cells [SOEC] and SOFC modes) were compared with more conventional cells between 800°C and 700°C and for various gas flow rates (12, 18, and 24 NmL min −1 cm −2 ). Distribution of relaxation time (DRT) analysis from electrochemical impedance spectroscopy (EIS) data highlights the effect of porosity and the oxygen electrode on the electrochemical performances. Finally, the work on support porosity and the nanostructured oxygen electrode demonstrated the most significant improvement in current density at 1.3 V and 700°C, under high gas flow rates (24 NmL min −2 cm −2 ). In this condition, the gain was 15.0% compared to the conventional cell.
ABSTRACT Microbial fuel cells (MFCs) are bioelectrochemical systems that convert chemical energy from organic substrates into electricity through microbial metabolism. Recently, miniaturized MFCs have attracted increasing interest since reducing device size can potentially increase surface‐area‐to‐volume ratio and decrease diffusion distance while supporting integration with microfluidics and low‐power electronics. Moving these devices from stand‐alone power generation devices toward field deployable self‐sustained bioelectronic platforms would require system level optimization involving three critical aspects: (i) novel anode materials and architectures to enhance performance through promoting rapid biofilm formation, (ii) cathode materials and oxygen reduction reaction (ORR) catalysts, which are responsible for stabilizing power generation and microbial activity, and (iii) miniaturized intricate device designs that offer innovative stacking schemes, advanced fabrication techniques, and biosensing operation. We summarize state‐of‐the‐art strategies that can be implemented for anode optimization (such as nanostructuring, three‐dimensional [3D] scaffolds, and surface functionalization), discuss ORR, and compare the performance of micro‐MFC platforms reported in recent literature in terms of power generation and usability in biosensing applications. Finally, we highlight engineering bottlenecks, including durability, membrane or separator limitations, and cost‐effective fabrication, and propose practical design directions to move miniaturized MFCs from proof‐of‐concept demonstrations to robust, application‐specific energy sources and biosensing devices.
ABSTRACT Existing air supply control approaches for proton exchange membrane fuel cell (PEMFC) systems calibrate the optimal oxygen excess ratio (OER) offline and apply it as a reference trajectory for online tracking, which fails to compensate for net power degradation caused by stack aging, membrane humidity variation, or stack temperature fluctuation. Therefore, this paper proposes a novel air supply control method with prescribed performance and online net power optimization for the PEMFC system. First, a prescribed‐time observer is designed to provide accurate OER estimation within a guaranteed convergence time window. Second, an adaptive reference governor is developed to correct the nominal OER reference online, with the calibration‐referenced net power deviation serving as one of the correction‐enabling conditions, without requiring gradient computation or perturbation injection. Third, a per‐interval reset prescribed performance controller is constructed via a two‐step backstepping procedure, and the performance boundary can be re‐initialized at each load transient event to prevent controller singularity under repeated load steps. The hardware‐in‐the‐loop (HIL) experimental results demonstrate that the mean net power achieved by the proposed method increased by 4.67% compared to the traditional one under simulated stack‐aging conditions, no boundary violations throughout all HIL tests, and robust control performance under parameter perturbations.
ABSTRACT Two‐dimensional metal carbide‐based MXenes, particularly Ti 3 C 2 T x , have garnered significant attention as potential alternatives to noble metal‐based electrocatalysts for water splitting reaction due to their high electrical conductivity, tunable surface chemistry, and large surface area. In this study, we report the Ti 3 C 2 T x /NiCo 2 O 4 nanohybrid catalyst for efficient overall alkaline water electrolysis. The hybrid architecture comprised of multi‐layered Ti 3 C 2 T x nanosheets uniformly decorated with NiCo 2 O 4 nanoparticles, enables enhanced charge transport and maximizes electrochemical active surface area, thereby enhancing electrocatalytic performance for both HER and OER in alkaline media. Furthermore, the Ti 3 C 2 T x /NiCo 2 O 4 nanocomposite exhibits a low overpotential of 191 and 321 mV@10 mA cm −2 for HER and OER, respectively. Corresponding Tafel slopes of 80 and 75 mV dec −1 further indicate favourable reaction kinetics. In a two‐electrode configuration, the composite achieves an overall water splitting cell voltage of 1.71 V at 10 mA/cm −2 , highlighting its bifunctional electrocatalytic capability. Moreover, the nanohybrid demonstrates excellent long‐term stability, maintaining consistent performance over 12 h of continuous operation. This work provides a rational tailoring strategy for engineering cost‐effective and efficient electrocatalyst for overall water splitting, leveraging the synergistic interactions between MXene nanosheets and spinel metal oxide nanostructures.
