XRD Case Study: Phase identification of bismuth nanowires

Figure 1. Phase ID confirming the formation of different Bi phases

Laboratory synthesised novel catalysts or functional materials can be in a variety of forms, such as thin films, foams or nanowires and often are made in very limited quantities. The modern Powder X-Ray Diffraction (PXRD) diffractometers on the Monash X-Ray Platform (MXP) collect data in a reliable, quick and convenient way to directly characterise the crystalline structure of newly synthesised catalysts and/or functional materials.

A huge amount of research effort has, and continues to be, devoted to solving the energy and environmental crisis arising from excessive consumption of fossil fuels. Electrocatalytic reduction can offer an attractive solution to the CO₂ related issues, with the possibility of storing renewable energy in chemical bonds and producing carbon-neutral fuels. Formic acid or formate is a common CO₂ reduction reaction product and is an important chemical feedstock and a promising fuel for fuel cells. Metallic bismuth (Bi) is an electrocatalyst that promotes CO2 reduction to formate. However, a substantial overpotential is needed to achieve a high formate faradaic efficiency along with a large catalytic current density, and this hinders its practical application. In this work, a facile strategy has been developed to obtain lattice-dislocated Bi nanowires on copper foam (Cu foam@BiNW) through in situ electrochemical transformation of an electroless plated Bi film on copper foam after thermal treatment in air. The Cu foam@BiNW is found to be a highly active electrocatalyst for CO2 reduction to formate at a low overpotential.

The three Bruker D8 Advance or Advance Eco diffractometers on the MXP are all designed in Bragg-Brentano geometry and equipped with high speed position sensitive detectors with energy discrimination capability. In this case, the PXRD pattern was collected using a Cu Ka X-ray source and was used to confirm the formation of Bismuth phase, the further calcinated Bi2O3 phase and finally the formation of Bismuth nanowire (BiNW) phase. PXRD was also used to confirm the stability of the BiNW phase after long-term electrolysis (12hrs).

Among the Monash X-ray Platform’s diverse and large user base, a significant number, including researchers from Chemistry, Chemical Engineering, and Materials Science and Engineering, are working on new functional materials, including new catalysts and energy materials. The MXP provides XRD instrumentation and services to facilitate the reliable, direct characterisation of these new materials to confirm target phases, or structures in a fast and convenient way.

Data and images reproduced courtesy of Zhang, X, Sun, X, Guo, SX, Bond, AM & Zhang, J 2019, 'Formation of lattice-dislocated bismuth nanowires on copper foam for enhanced electrocatalytic CO2 reduction at low overpotential', Energy and Environmental Science, vol. 12, no. 4, pp. 1334-1340. https://doi.org/10.1039/c9ee00018f