PEM water electrolysis cells with catalyst coating by atomic layer deposition

The limited annual mining capacity and high costs of platinum metal group catalysts (PMG) are confining the production of hydrogen from PEM electrolysis. Therefore, a significant reduction of catalyst needs is crucial to reduce system costs and increase production capacity. This study demonstrates the feasibility of a PEM water electrolysis cell design using porous transport electrodes (PTE) with catalyst coating by atomic layer deposition (ALD) and operation in 1 mol/L sulphuric acid at 60 °C. Though the catalyst loading has been reduced to 0.12 mg/cm² iridium on the anode and 0.28 mg/cm² platinum on the cathode, a current density of 168 mA/cm² and mean high mass activity of 1400 A/g iridium could be achieved at 1.7 V. The characterization of three high loading PTE cells is combined with a detailed overpotential analysis from polarization curve fits and demonstrates a reproducible cell setup. Further analysis steps show an increasing cell performance with increasing coating cycle numbers and the consistency of the anode performance in the three electrode setup with the complete cell. The ALD coated PTE design turns out to be a promising candidate for catalyst loading reduction in PEM electrolysis.     

Degradation studies of proton exchange membrane water electrolysis cells with low platinum group metals – Catalyst coating achieved by atomic layer deposition

Activity and durability of a polymer electrolyte membrane (PEM) water electrolysis single cell, assembled with porous transport electrodes (PTEs) with a low catalyst loading were investigated for 500 h. A current density of 160 mA/cm² and a high mass activity of 1368 A/g_Ir were achieved while operating at 60 °C with 1 mol/L sulfuric acid. The degradation of the cell was characterized using different electrochemical and physicochemical methods before, during and after operation of the electrolysis cell and a mean degradation rate for the cell of 67 μV/h was determined at 15 mA/cm². To the best of our knowledge this is the first time that long-term performance of a PEM water electrolysis cell assembled with PTEs coated by ALD is investigated.     

Ru nanoparticles loaded on tannin immobilized collagen fibers for catalytic hydrolysis of ammonia borane

A kind of Ru-based catalyst was prepared by using a natural polyphenolic polymer (bayberry tannin, BT) immobilized on collagen fiber (CF) as the stabilizer and carrier of Ru nanoparticles (NPs) and characterized to detect its main physicochemical properties. The CF-BT-Ru catalyst was found to be in an orderly fiber morphology with Ru NPs with about diameter of 2.6 nm highly distributed on the surface. The research on catalytic activity of CF-BT-Ru focused on the hydrolysis of ammonia borane (AB) to produce hydrogen. The influences of Ru loading, Ru dosage, AB concentration and temperature on the catalytic AB hydrolysis were investigated in detail, and the related thermodynamic parameters (activation energy (E_a), activation entropy (△S), activation enthalpy (△H) and Gibbs free energy (△G)) were calculated. The experimental results indicated that CF-BT-Ru exhibited high catalytic activity. Its turnover frequency (TOF) was as high as 322 ${\text{mol}}_{{\text{H}}_2}?{\text{mol}}_{\text{Ru}}^{?1}?{\text{min}}^{?1}$ and E_a was as low as 32.41 kJ mol^?1 for AB hydrolysis. Moreover, CF-BT-Ru exhibited satisfied reusability and stability. Its activity lost only one-fifth and no obvious agglomeration and leakage of Ru NPs were found after repeated use for 5 times.     

The comparison of direct borohydride-hydrogen peroxide fuel cell performance with membrane electrode assembly prepared by catalyst coated membrane method and catalyst coated gas diffusion layer method using Ni@Pt/C as anodic catalyst

Carbon supported Ni@Pt nanoparticles are synthesized using sodium dodecyl sulphate (SDS) and sodium borohydride (NaBH₄) as a structure-directing and reducing agents, respectively. The metal loading in synthesized nanocatalyst is 20 wt% and the ratio of Ni:Pt in the nanocatalyst is 1:1. The structural characterizations and morphologies of Ni@Pt/C nanocatalyst are investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The electrocatalytic activity of Ni@Pt/C catalyst toward borohydride $\left({\text{BH}}_4^{?}\right)$ oxidation in alkaline medium is studied by means of cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA). The results show that Ni@Pt/C catalyst has superior catalytic activity toward borohydride oxidation (8825.38 mA mg Pt^?1). The Membrane Electrode Assembly (MEA) used in fuel cell set-up is fabricated with catalyst-coated membrane (CCM) and catalyst coated gas diffusion medium (CCG) techniques. The effect of two MEA performances on current–voltage (I–V) and current–power density (I–P) curves in the direct borohydride-hydrogen peroxide fuel cell was investigated using Pt/C 0.5 mg cm^?2 as cathode catalyst and Ni@Pt/C 1 mg cm^?2 as anode catalyst. The influence of cell temperature, sodium borohydride and hydrogen peroxide concentration on the I–V and I–P is determined. The results show that the maximum power density in MEA prepared using CCM method (CCM-MEA) is 68.64 mW cm^?2 at 60 °C, 1 M sodium borohydride and 2 M hydrogen peroxide (H₂O₂) that is higher than MEA prepared using CCG method (CCG-MEA). The impedance results show that with increasing temperature and discharging current, the overall anodic and cathodic charge transfer resistances reduce.     

Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis?

Proton exchange membrane water electrolysis (PEMWE) is a key technology for future sustainable energy systems. Proton exchange membrane (PEM) electrolysis cells use iridium, one of the scarcest elements on earth, as catalyst for the oxygen evolution reaction. In the present study, the expected iridium demand and potential bottlenecks in the realization of PEMWE for hydrogen production in the targeted GW a^?1 scale are assessed in a model built on three pillars: (i) an in-depth analysis of iridium reserves and mine production, (ii) technical prospects for the optimization of PEM water electrolyzers, and (iii) PEMWE installation rates for a market ramp-up and maturation model covering 50 years. As a main result, two necessary preconditions have been identified to meet the immense future iridium demand: first, the dramatic reduction of iridium catalyst loading in PEM electrolysis cells and second, the development of a recycling infrastructure for iridium catalysts with technical end-of-life recycling rates of at least 90%.