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In this work, the effect of a predeposited Co-Ni layer on the catalytic activity and long-term durability of the quaternary Co-Ni-P-B catalyst for the hydrogen evolution reaction (HER) is investigated. To study the effect of predeposition of the Co-Ni layer for the Co-Ni-P-B catalyst, both Co-Ni-P-B/Co-Ni/Cu and Co-Ni-P-B/Cu catalysts are prepared. The current density for HER of the Co-Ni-P-B/Co-Ni/Cu catalyst at −0.5 VRHE is 36.1% higher than that of Co-Ni-P-B/Cu in 0.5 M H2SO4 solution at 18 °C. This is because the porous morphology of the Co-Ni-P-B/Co-Ni/Cu catalyst leads to a 10.6% larger electrochemical surface area and higher atomic ratio for both the P and B contents, which act as a proton acceptor and a supplier of electrons to the d orbital of the transition metals, respectively, compared to Co-Ni-P-B/Cu on the catalytic surface. Furthermore, the Co-Ni-P-B/Co-Ni/Cu catalyst retains 94.5% of the catalytic activity during durability test of 1 h owing to its higher adhesion strength between the substrate and catalyst and rougher morphology, whereas the Co-Ni-P-B/Cu catalyst shows a retention of only 64.4%.

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.

Herein, we study the effects of a nanometrically uniform array of Ag nanoparticles (AgNPs) on the electrochemical nucleation and electrodeposition behavior of Li metal anodes (LMAs). The AgNP array is grown directly on the surface of commercial planar Cu current collectors (CCs) using a thermal evaporation system by limiting the growth of Ag thin films to an island stage. When the film is grown to an evaporation thickness of 3 nm, AgNPs with an average diameter of 11.4 nm are uniformly formed on the surface of Cu CCs. On the electrochemical nucleation of Li, the uniformly distributed AgNPs effectively provide nucleation sites for Li deposition and hence increase the nuclei density and spatial uniformity and decrease the size of the nuclei and nucleation overpotential. As a result, a dendrite-free, dense and pebble-like morphology of Li deposits is formed, and a high Coulombic efficiency (CE) of 98.5% is obtained during 100 cycles of the repeated electrodeposition and stripping of Li at a current density of 0.5 mA cm−2 for 1 mAh cm−2. In contrast, the cycle life of pristine Cu is limited to the 83rd cycle in the same testing environment.

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.