Hydrogen Production by Hydrolysis of Recycled Aluminum and Reagent Recovery by Electrolysis of the By-Product

Summary

This study demonstrates the generation of hydrogen from aluminum cans via alkaline hydrolysis and the electrochemical recovery of aluminum and sodium compounds, enabling a recyclable, closed-loop reagent system.

Abstract

Hydrogen is a promising energy carrier for achieving net-zero greenhouse gas emissions; however, its storage and distribution remain a challenge. This study shows a reproducible closed-loop protocol for on-demand hydrogen generation using aluminum beverage cans via alkaline hydrolysis, followed by electrochemical recovery of aluminum and sodium compounds from the reaction by-products. Aluminum cans are pretreated using combined thermal and chemical steps to remove polymer coatings and improve reactivity. Hydrogen is produced using sodium hydroxide solutions (3–5 M) and collected volumetrically, reaching a purity of 93.66% by volume, as determined by gas chromatography. The resulting sodium aluminate solution is processed in a two-compartment electrochemical cell, allowing precipitation of aluminum hydroxide (gypsite and bayerite phases) and the regeneration of sodium hydroxide at a concentration of 4.98 M ± 0.03 M. The energy consumption for the electrochemical recovery of aluminum hydroxide corresponds to an energy efficiency of 0.632 Wh･g⁻¹. This work provides a practical framework for integrating hydrogen production with aluminum waste recovery in circular energy systems.

Introduction

The transition to net-zero greenhouse gas emissions requires the deployment of energy carriers that uncouple energy generation from consumption while enabling the large-scale integration of renewable resources. Currently, large-scale energy storage is dominated by pumped hydro, which accounts for more than 90% of global energy storage capacity. Other storage technologies, such as lithium-ion batteries, compressed air, and flywheels, remain limited in their scalability and cost-effectiveness for grid applications^1,2,3.

In this way, hydrogen is widel....

Protocol

1. Pre-treatment of aluminum sheets

1. Initial preparation of aluminum cans
   Aluminum beverage cans (473 mL) were collected and thoroughly rinsed with tap water and dishwashing detergent to remove residual liquids and sugars. The cans were subsequently rinsed with deionized water and allowed to air dry at room temperature. The top and bottom ends of each can were removed using metal scissors, retaining only the cylindrical body. The aluminum body was then cut and flattened into sheets, which were further divided into pieces of the desired size (4 mm² or 1 cm²).
2. Thermal pre-treatment with acetone
   Th....

Results

The success of the pre-treatment of recycled aluminum cans is confirmed by visual inspection and X-ray diffraction (XRD) analysis (Figure 3). After combined treatment with acetone and calcination, the aluminum surfaces exhibited a uniform metallic appearance. Although the dominant diffraction peaks correspond to metallic aluminum (JCPDS 04-0787), additional minor features are assigned to residual surface oxides, particularly in samples subjected to incomplete pre-treatment or in regions wher.......

Discussion

Previous studies have described various pre-treatment and activation strategies to improve aluminum hydrolysis in water, including mechanical and mechanochemical activation (e.g., ball milling or magnetic activation), galvanic activation with metal additives, liquid metal activation, chemical etching, and heat treatments^{30,31,32,33,34}. Although mechanochemical.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone, ACS reagent (≥99.5%)	Jalmek	A0425	Removal of paint and polymeric coatings
Aluminum beverage cans (473 mL)	Local collection	N/A	Post-consumer aluminum feedstock
Analytical balance	Boeco	BAS 31 Plus	Mass measurements
Benchtop autoclave	Ecoshel	CVQ-280d	Thermal pretreatment
Data acquisition software	In-house programmed	N/A	Temperature and pressure logging
DC power supply	Matrix	MPS-3002L-3	Electrolysis operation
Deionized water (18.2 MΩ·cm @ 25°C)	Millipore Milli-Q (in-house)	N/A	Preparation of solutions and washing steps
Desiccator	Glass laboratory type	N/A	Cooling and moisture control
Drying oven	Binder	RF115-UL	Drying aluminum hydroxide
Gas chromatograph	Agilent Technologies	7890B	Hydrogen purity analysis
Graham condenser (300 mm)	N/A	N/A	Primary condenser
Graphite electrode (anode)	Fuel Cell Earth	Isomolded Graphite Plate	Electrochemical oxidation
Ice / ice bath	Local supply	N/A	Cooling condenser to ~0°C
Inverted burette (1000 mL)	Custom-built	N/A	Volumetric hydrogen measurement
Muffle furnace	Yamato	FO100CR	Calcination of aluminum samples
Nafion 212 membrane	DuPont	NRE 212	Proton exchange membrane
pH buffer solutions (CRM)	Fermont	S1015, S1025, S1035	Calibration of pH meter
pH meter	Thermo Scientific	Orion Star A211	Monitoring catholyte pH
Phenolphthalein indicator	Sigma-Aldrich	319236	Endpoint detection in titration
Potassium hydrogen phthalate (CRM)	MilliporeSigma Supelco	11-101-5732	Acid–base titration standardization
Pressure sensor	Bosch	BMP180	Monitoring reactor pressure
Secondary condenser	Custom-built	N/A	Moisture removal from hydrogen gas
Sodium hydroxide (NaOH) pellets	Fermont	36902	Preparation of alkaline solutions (3–5 M)
Stainless steel electrode (cathode)	Fuel Cell Earth	304 SS 120 Mesh	Electrochemical reduction
Temperature sensor & data logger	Custom-built	N/A	Monitoring hydrolysis reaction
Three-neck round-bottom flask (150 mL)	DesChem	N/A	Hydrogen generation reactor
Two-compartment electrochemical cell	Custom-built	500 mL per cell	Electrochemical recovery
Ultrasonic bath	Branson	1510	Acetone-assisted paint removal
X-ray diffractometer (XRD)	Rigaku	Ultima IV	Phase identification
XRD analysis software	Manufacturer-provided	N/A	Phase identification