Complex hydrides are metallic alloys that can absorb and then release hydrogen. Sandia researchers have developed a promising new class of hydrides that operate at pressures and temperatures close to ambient conditions, making them highly promising for developing future onboard hydrogen storage systems.

Hydrogen ion signal recorded by mass spectrometer during a thermal desorption experiment on metal hydride sample.

Achieving hydrogen storage at low pressures is widely considered one of the most important hurdles for the commercial success of hydrogen as a transportation fuel, due in part to weight and volume constraints imposed on vehicles. Currently, no material exists that can be used to construct a fuel tank capable of storing a sufficient quantity of hydrogen fuel at low pressure and near-ambient temperature.

Sandia scientists and engineers are seeking a more detailed understanding of the chemical and physical processes governing hydrogen uptake and release in these novel solid materials. By using optical diagnostics, such as infrared spectroscopy, in conjunction with mass spectrometry, we are able to probe the chemical bonding of hydrogen at the vapor-solid interface, as well as characterize the uptake and release kinetics that govern system behavior. Our goal is to resolve the mechanistic details of hydrogen adsorption and desorption reactions in complex hydride materials, with a primary emphasis on the effects of additives such as catalysts, as well as to understand key issues associated with various methods of material synthesis.

DRIFT spectra of adsorbed water produced after reacting metal hydride with oxygen.

Our approach involves conducting experiments on small sample volumes under realistic operating conditions. Experiments are performed in a miniature high-pressure, high-temperature flow reactor equipped with advanced diagnostics. The flow reactor is capable of operating at 100 bar and temperatures in excess of 800 K, conditions required for adsorbing hydrogen into certain families of hydride materials. Optical access to the sample is achieved through a zinc selenide dome configured for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Gases exiting the reactor are sampled in real time by mass spectrometry.

High pressure and temperature flow cell with optical access for conducting Diffuse Reflectance Infrared Fourier Transform (DRIFT) measurements.

The analytical system is used to conduct adsorption/desorption experiments to determine hydrogen storage capacity, as well as temperature-programmed reaction experiments designed to measure rates of hydrogen uptake and release. The DRIFTS measurement provides mechanistic detail by way of monitoring the evolution of surface-bound stable intermediates through vibrational spectroscopy.

Contact:
Tony McDaniel
amcdani@sandia.gov
(925) 294-1440