Electrolessly Deposited Transition Metal Phosphide Catalysts for Hydrogen Generation from Hydrolysis of Sodium Borohydride

Hydrogen (H₂) is regarded as a significant and environmentally sustainable energy carrier due to its high energy efficacy, zero toxicity, and pollution-free combustion, making it a potential long-term substitute for fossil fuels. However, efficient hydrogen storage remains a challenge. Among chemical hydrides, sodium borohydride (NaBH₄) is attractive due to its high hydrogen content (10.8 wt%) and environmentally favorable hydrolysis products. Nevertheless, its hydrolysis in water is slow and requires efficient catalysts to enhance hydrogen generation. Herein, cobalt-phosphorus (Co-P) catalysts with varying phosphorus contents were investigated for hydrogen generation via the hydrolysis of alkaline NaBH₄ solutions. The catalysts were fabricated on copper substrates through an electroless metal plating technique, with sodium hypophosphite (NaH₂PO₂) utilized as the reducing agent. The Co-P catalysts with different P amounts of 3, 5, 8, and 11 wt.% were obtained. The morphology, structure, and elemental composition of the prepared catalysts were characterized using a variety of analytical techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).

The hydrogen generation rate was evaluated in a solution containing 5 wt.% NaBH₄ and 0.4 wt.% NaOH at temperatures ranging from 313 to 343 K. The results indicate that Co-P catalysts have notable catalytic activity toward the hydrolysis of NaBH₄. The hydrogen generation rate exhibited a range from 1 to 10 L min^-1 g^-1 at 343 K, while the activation energy demonstrated a range from 49 to 85 kJ mol^-1, dependent on the phosphorus content. Specifically, the Co-P catalyst containing 11wt.% phosphorus was identified as the most efficient catalyst, exhibiting a hydrogen generation rate of 10.05 L min^-1 g^-1 at 343K. The excellent catalytic performance and cost-effectiveness of the electroless-deposited Co-P catalysts highlight their potential for efficient hydrogen production via NaBH₄ hydrolysis.