The Hydrogen Generation From NaBH₄ Solution By Using Electroplated Co-based Film Catalysts

Recently, the researches of fuel cells became increasingly important due to the depletion of fossil fuel. In this regard, developing efficient in situ hydrogen supply technique was one of the key issues in improving fuel cell feasibility. Using metal hydrides with high hydrogen storage capacity, such as NaBH4 was proposed to be a promising way.In this work, we produced four amorphous alloy catalysts and studied the the catalyst for hydrogen generation from alkaline NaBH4 solution. We investigated the importance factors which impact the hydrogen generation rate. And the work is been divided into four parts:1. We prepared the Co-P catalysts electrodeposited from Co-P bath under several of Na2H2PO2 concentrations, and investigated the hydrolysis of NaBH4 solution by these catalysts. The experimental results showed that the hydrogen generation properties of the electrodeposited Co-P catalysts in alkaline NaBH4 solution largely depended on NaH2PO2 concentrations. The deposited Co-P alloys exhibited amorphous structure, and the highest hydrogen generation rate of 5965 mL (min g-catalyst)-1 was achieved when 1.0M NaH2PO2 was used. This rate was 1.4 folds higher than the reported electroless-deposited Co-P catalysts. Furthermore, the activation energy for hydrolysis of NaBH4 was as low as 23.9 kJ mol-1. The durability of the Co-P catalyst was also tested and showed stable activity in 5 cycles.2. The amorphous Co-Ni-P films were electroplating on Cu sheets. The effects of NiSO4 concentrations on the deposit plating rate and the catalytic activities for NaBH4 hydrolysis were investigated. The surface morphology and phase structure of the deposited Co-Ni-P films were characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The composition was analyzed by energy dispersive spectrometer (EDX). Experimental results showed that adding NiSO4 in Co-P bath could increase the deposition rate. When 0.01M of NiSO4 was used, the highest deposition rate and the highest hydrogen generation rate of 3636 mL (min g-catalyst)-1 were obtained. The activation energy (Ea) for the NaBH4 hydrolysis was 38 kJ mol-1, which was comparable to the value of noble metal catalysts. XPS was used to gain insight into the impact of Co, Ni and P in Co-Ni-P film catalysts. Due to the interacting with Ni and Co, the lower binding energy peak of P shifted negatively by 1.4 eV. Hence, this low-cost and reusability of the Co-based catalysts is an economically viable and excellent for alkaline hydrolysis of NaBH4.3. Amorphous Co-W-P catalysts were prepared on Cu substrates by electrodeposition, which have been investigated as the catalyst for hydrogen generation from alkaline NaBH4 solution. The surface morphology and chemical composition of the as-prepared Co-W-P catalysts were analyzed in relation to the cathodic current density and the electrodeposition time. The experimental results revealed that the optimized experimental parameter was at cathodic current density of 0.1 A cm-2 and deposition time of no longer than 8 min. The hydrogen generation rate for the optimized Co-W-P catalyst is measured to be 5000 mL (min g-catalyst)-1 at 30℃. From hydrogen generation tests in solutions with the various concentrations of NaBHU and NaOH, the optimum concentration were 10 wt.% NaBH4 and 10 wt.% NaOH. Furthermore, the as-prepared catalyst also showed good cycling capability and the activation energy for hydrolysis of NaBH4 by the Co-W-P catalyst was calculated to be 22.8 kJ/mol, which was lower than other reported Co-based catalysts.4. The hollow granular cobalt-molybdenum-phosphorus films with different molybdenum were deposited on copper sheet by electroplating. The films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The pattern of XRD indicated that the films showed amorphous structure and the surface were constituted of Co-Mo-P hollow particle. The hydrogen bubbles generated during electroplating as the activity template. The hysteresis loops of the films were measured by a vibrating sample magnetometer (VSM), the soft magnetic signature emerged with the coercivity was 15.25Oe when the concentrations of Na2MoO4 was 0.16M and the saturation magnetisation was 80.4 emu/g when the concentrations of Na2MoO4 was 0.1M. The loop shift was observed, and shift can be as large as-27.55Oe when Na2MoO4 was 0.16M. The experimental results revealed that the optimized experimental parameter was at the Na2MoO4 was 0.16M, cathodic current density of 0.1 A cm-2 and deposition time of 12 min. The highest hydrogen generation rate [2710 mL (min g-catalyst)-1] obtained when the catalyst was used at 4 cycles. This means the surface of catalyst was covered oxydic films during the electrodeposition.