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The effect of Fe content in electroless-deposited Co Ni-Fex-P alloy catalysts (x = 5.5–11.8 at.%) from the hydrolysis of NaBH4 is investigated in alkaline sodium borohydride solution. The electroless-deposited Co Ni Fe5.5-P and Co Ni Fe7.6-P alloy catalysts are composed of flake-like micron particles; however, with an increase in Fe content to 11.8 at.%, the flake-like morphology is changed to a spherical shape and the crystal structure of the electroless-deposited Co Ni Fe P catalyst is transformed from FCC to BCC. Among all the Co Ni-Fex-P alloy catalysts, the Co Ni-Fex-P (x = 7.6 at.%) catalyst has the highest hydrogen production rate of 1128 ml min−1 g−1catalyst in alkaline solution containing 1 wt% NaOH + 10 wt% NaBH4 at 303 K. For the optimized catalyst, the activation energy of the hydrolysis of NaBH4 is calculated to be 54.26 kJ mol−1. Additionally, in this work, we report a new hydrolysis using Mg(BH4)2 and Ca(BH4)2. As a result, the Mg(BH4)2 is stored unstably in an alkaline solution, whereas the Ca(BH4)2 is stored stably. When optimizing the hydrogen production kinetics from the hydrolysis of Ca(BH4)2, the rate is 784 ml min−1 g−1catalyst in 10 wt% NaOH + 3 wt% Ca(BH4)2 solution.

Due to the ban on the use of food waste as wet swine feed after the outbreak of African swine fever (ASF), 2900 tons/day of food waste and 1083 tons/day of food waste leachate were additionally generated. As an alternative treatment method for food waste leachate, the input of food waste leachate on weekends (5% of food waste leachate inflow, 100 tons/day) and its increased input (merge ratio 21.7%, 227.01 tons/day → 27.8%, 453.71 tons/day) into the digesters operated in a public sewage treatment plant were investigated. Additionally, the feasibility of the method was evaluated by analyzing the operation parameters, evaluating the operation efficiency, and identifying other environmental effects on the sewage treatment plant. In the case of input on weekends, the organic matter decomposition rate and gas production rate decreased by 8.0% and 9.5%, respectively, although the input on weekends was judged to be feasible, considering that the inflow into the WWTP increased by up to 206% due to the long-term (7 weeks) monsoon. In the case of the increased input of food waste leachate, the organic matter decomposition and gas production rates increased by 2.5% and 4.8%, respectively, compared with before the increased input. The results of this study confirmed that the additional input of food waste leachate into existing biogasification facilities is feasible. When performed in a stable manner, the use of food waste for anaerobic digestion is considered an appropriate alternative treatment method to wet feed. This will lead to technological and industrial development.

In this work, we study the dependence of water content on the carbon corrosion reaction by applying an external potential (1.4 V vs RHE) under saturated and low (30%) relative humidity (RH) conditions via a transmission line model (TLM)-based impedance analysis in a polymer electrolyte membrane fuel cell (PEMFC). High potentials inducing carbon corrosion reaction cause electrode thinning, make the supporting carbon structure less porous, decrease the electrochemical surface area (ECSA), and dehydrate the ionomer, leading to fast performance decay in the cell. Particularly, in this work, we discuss the main cause of performance decay in PEMFCs in view of the structural deformation of supporting carbon using the ionic resistance and double layer capacitance in non-faradaic impedance and charge transfer resistance in faradaic impedance to elucidate the different degradation behaviors of membrane electrode assembly (MEA) under saturated and low humidity (RH 30%) conditions. As a result, it is confirmed that carbon corrosion severely changes the structural properties of the supporting carbon, such as pore depth and circumference, and the specific pore deformation with the evolution of oxygen-containing functional groups on the carbon surfaces subordinately induces the severe degradation in cell performance with the water drainage issues, namely, flooding.

Herein, electrochemical impedance spectroscopy (EIS) analysis is performed under low-relative humidity conditions (RH30) to use the transmission line model (TLM) to emphasize ionic resistance in a polymer electrolyte membrane fuel cell (PEMFC). In particular, EIS measurement under RH30 based on the TLM (TLM-RH30) facilitates a focus on the inherent properties of the membrane electrode assembly (MEA) by deliberately limiting and separating the proton conductivity from the complicated impedance circuits. To verify the feasibility of TLM-RH30 in EIS analysis, the dehydration degradation test of a PEMFC is performed under RH 30% for more than 600 h. From the electrochemical results obtained using TLM-RH30, the degradation mechanism can be sequentially deconvoluted with respect to operating time; (i) first, an increase in ionic resistance occurs, followed by (ii) membrane thinning and (iii) reverse current decay inducing severe cathode deterioration due to carbon corrosion. The sequential degradation mechanism under dehydration is also supported by the surface analysis results of deteriorated MEAs using SEM TEM, EDS, XRD, and XPS. It is notable that EIS analysis adopting TLM-RH30 enable an accurate diagnosis by establishing the sequential degradation causes in each MEA component, such as the ionomer, membrane, and catalyst layer, in a PEMFC.