Johnson Matthey Technology Review - Volume 65, Issue 1, 2021

This first part of a two-part commemoration of the life and work of Robert D. Gillard begins with a biographical outline which provides a context for his chemical achievements. He was awarded a State Scholarship and after his National Service in the Royal Air Force he went up to St Edmund Hall, Oxford, to read Chemistry. There follows a chronological account of his career in Chemistry starting with his undergraduate days in Oxford, where a Part II project with Dr Harry Irving on alkaline earth and cobalt complexes proved seminal. His PhD research at Imperial College, London in the Geoffrey Wilkinson group broadened his experience into the then poorly developed chemistry of rhodium and other platinum group metal complexes. Gillard next went to Sheffield University as a Lecturer where he developed independent research while continuing to work on earlier topics. There followed a move to Canterbury as a Reader at the University of Kent. In his particularly productive seven years there with a large research group he widened his experience further, expanding his interests in such areas as the optical properties of transition metal complexes, considering biological and medical relevance, and increasing the range of metals and ligands he investigated. His subsequent time at Cardiff and then into retirement will be covered in the second part of this commemoration.

The second part of this commemoration covers the final stage of Robert Gillard’s career as Professor of Inorganic Chemistry at Cardiff University and his time in retirement. At Cardiff he built on earlier work while extending his scientific interests still further into mineralogical and archaeological chemistry, and even into forensic dentistry. Coordination chemistry research continued and included the polysulfide S5 chain as a bidentate ligand in the all-inorganic cyclic PtS5 unit and the rhodium(III) complex [Rh(S5)3]^3–. His penchant for discussion led him into several controversies, particularly over his ‘covalent hydration’ hypothesis of coordinated nitrogen-carbon double bonds in metal complexes which included those with platinum and 2,2’-bipyridine. He travelled widely attending international conferences and giving lectures. Research collaborations continued throughout his time at Cardiff and in particular he had many strong links with Portugal, both with colleagues there and as supervisor of Portuguese higher degree students at Cardiff. His years in retirement were spent in finalising his research legacy, in continuing to read historical literature, both chemical and otherwise, and in following his musical interests that had included many years singing in the Cwmbach Male Voice Choir.

Platinum-based knitted gauzes are the most efficient catalysts for the production of nitric oxide, as a precursor to the manufacture of nitric acid and caprolactam. Decades of research and optimisation have resulted in a greater understanding of ammonia oxidation kinetics and associated metal movement within these catalyst packs, along with the development of beneficial binary and ternary alloys. The design of a pack has evolved from the simple addition or removal of metal to modelling the optimal installed metal content and distribution. This review discusses the fundamental kinetics and in situ metal loss for ammonia oxidation catalysts in nitric acid applications and outlines how they can, in conjunction with prevailing platinum group metal (pgm) market conditions and plant key performance indicators (KPIs), influence the optimal catalyst design.

The thermodynamic properties were reviewed by the author in 1995. A new assessment of the enthalpy of fusion at 68.0 ± 1.7 kJ mol⁻¹ leads to a revision of the thermodynamic properties of the liquid phase and although the enthalpy of sublimation at 298.15 K is retained as 788 ± 4 kJ mol⁻¹ the normal boiling point is revised to 5565 K at one atmosphere pressure.

Palladium based membranes are widely used for supplying ultra-high purity hydrogen to a polymer electrolyte fuel cell (PEFC) installed on small vehicles and various electronic devices. Compared to pressure swing adsorption (PSA), the use of palladium based membrane is more economical for small size (small capacity) applications. The transportation of hydrogen through a palladium based membrane is governed by Sieverts’ Law and quantified with Fick’s First Law. Since the 20th century, the fabrication of high-performance palladium based membrane for enhanced hydrogen recovery performance has become practical. However, along with the improvement in hydrogen recovery performance, concentration polarisation becomes unavoidable because hydrogen permeation flux starts to affect hydrogen concentration at the membrane surface. Various parametric studies have investigated the effects of membrane thickness, hydrogen molar fraction and total upstream and downstream pressures on concentration polarisation level. The influence of membrane temperature, permeability, type and number of species in the hydrogen mixture, diffusivity of the hydrogen mixture, system configurations and flow patterns are also reported and comprehensively reviewed in this paper. Part II will complete the presentation.

This article completes the presentation of various techniques reducing concentration polarisation in palladium based membranes for supplying ultra-high purity hydrogen to a polymer electrolyte fuel cell (PEFC), such as the implementation of baffles and the use of microchannel configuration. The present paper also reviews and reports the current methods for estimating hydrogen permeation flux under concentration polarisation influence, which will be a useful guide for academics and industrial practitioners.

The present article considers the lattice dynamical study of platinum by use of the Van der Waals three body force shell model (VTBFSM) due to high stiffness constant C11 and C12. The model uses the frequencies of the optical and vibrational branches in the direction [100] and phonon density of states (DOS). The study of phonon spectra is important in determining the mechanical, electrical and thermodynamic properties of elements and their alloys. The present model incorporates the effect of Van der Waals interactions (VWI) and three-body interactions (TBI) into the rigid shell model (RSM) with face-centred cubic (fcc) structure, operative up to the second neighbours in short range interactions. The available measured data for platinum agrees well with our results.

Developing novel hydrogen evolution reaction (HER) catalysts with high activity, high stability and low cost is of great importance for the applications of hydrogen energy. In this work, iridium-nickel thin films were electrodeposited on a copper foam as electrocatalyst for HER, and electrodeposition mechanism of iridium-nickel film was studied. The morphology and chemical composition of thin films were determined by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), respectively. The electrocatalytic performances of the films were estimated by linear sweep voltammograms (LSV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results show that iridium-nickel thin films were attached to the substrate of porous structure and hollow topography. The deposition of nickel was preferable in the electrolyte without the addition of additives, and the iridium-nickel thin film was alloyed, resulting in a high deposition rate for Ir42Ni58 thin film, and subsequently an increase of iridium content in the thin films of Ir80Ni20 and Ir88Ni12. Iridium-nickel thin films with Tafel slopes of 40–49 mV dec^–1 exhibited highly efficient electrocatalytic activity for HER. The electrocatalytic activity of iridium-nickel thin films showed a loading dependence. As the solution temperature increased from 20°C to 60°C, the hydrogen evolution performance of iridium-nickel thin films improved. The apparent activation energy value of Ir88Ni12 film was 7.1 kJ mol^–1. Long-term hydrogen evolution tests exhibited excellent electrocatalytic stability in alkaline solution.

Platinum-20% rhodium strengthened by oxides of zirconium and yttrium were prepared by solidification of platinum-rhodium-(zirconium)-yttrium powder which had been internally oxidised. After forging, rolling and annealing, 1 mm plates were obtained. Then the plates were mechanically ground to 50–70 μm from rolling-normal direction, followed by argon ion milling until a hole appeared on the centre of the foil to obtain samples which were characterised by transmission electron microscopy (TEM), combined with thermodynamic analysis. The existence of spherical ZrO2 and Y2O3 particles was verified with platinum and rhodium present as pure metals at the same time. It was found that the deformation behaviour of ZrO2 and Y2O3 particles was quite different during processing, where the former basically maintain their spherical shape and were bonded tightly to matrix, while the latter were compressed along normal direction and form two cracks on both sides of Y2O3 particles along the rolling direction. The differences in hardness and interface bonding properties of these two types of particles are supposed to be the main causes of different deformation behaviour during hot forging and cold rolling.

Deformation and fracture behaviour of cold drawing iridium wire under tension at room temperature is examined. High purity polycrystalline iridium was manufactured using pyrometallurgical technology. During the initial stage of cold rolling, iridium wire has its usual grain structure and exhibits brittle deformation behaviour: poor plasticity and brittle transgranular fracture (BTF). However, the wire begins demonstrating high plasticity including necking in spite of the brittle fracture mode when the lamellar structure has been formed in iridium during cold drawing.

PLATInum group metals Recovery Using Secondary raw materials (PLATIRUS), a European Union (EU) Horizon 2020 project, aims to address the platinum group metal (pgm) supply security within Europe by developing novel and greener pgm recycling processes for autocatalysts, mining and electronic wastes. The initial focus was on laboratory-scale research into ionometallurgical leaching, microwave assisted leaching, solvometallurgical leaching, liquid separation, solid phase separation, electrodeposition, electrochemical process: gas-diffusion electrocrystallisation and selective chlorination. These technologies were evaluated against key performance indicators (KPIs) including recovery, environmental impact and process compatibility; with the highest scoring technologies combining to give the selected PLATIRUS flowsheet comprising microwave assisted leaching, non-conventional liquid-liquid extraction and gas-diffusion electrocrystallisation. Operating in cascade, the PLATIRUS flowsheet processed ~1.3 kg of spent milled autocatalyst and produced 1.2 g palladium, 0.8 g platinum and 0.1 g rhodium in nitrate form with a 92–99% purity. The overall recoveries from feedstock to product were calculated as 46 ± 10%, 32 ± 8% and 27 ± 3% for palladium, platinum and rhodium respectively. The recycled pgm has been manufactured into autocatalysts for validation by end users. This paper aims to be a project overview, an in‐depth technical analysis into each technology is not included. It summarises the most promising technologies explored, the technology evaluation, operation of the selected technologies in cascade, the planned recycled pgm end user validation and the next steps required to ready the technologies for implementation and to further validate their potential.

BIORECOVER brings together diverse expertise with the goal of developing a new sustainable and safe process, essentially based on biotechnology, for selective extraction of critical raw materials (CRMs), rare earth elements (REE), magnesium and platinum group metals (pgms). The four-year European Union (EU) H2020 project involves 14 international partners from mining, microbiology, chemistry, engineering, metallurgy, sustainable process development, as well as CRM end-users. Starting from relevant unexploited secondary and primary sources of CRMs, BIORECOVER will develop and integrate three stages for CRM extraction: (a) removal of major impurities present in raw materials; (b) mobilisation of CRMs through use of microorganisms; and (c) development of specific technologies for recovering metals with high selectivity and purity that meet the quality requirements for reuse. Downstream processes will be developed and recovered metals will be assessed by end-users. Modelling and integration of the modular stages and economic and environmental assessment will be done to develop the most effective and sustainable process. This short feature describes the aims and approach, project technologies and intended outputs of the BIORECOVER project.