Approaching Industrially Relevant Current Densities for Hydrogen Oxidation with a Bioinspired Molecular Catalytic Material

Abstract

Integration of efficient platinum group metal (PGM)-free catalysts to fuel cells and electrolysers is a prerequisite to their large-scale deployment. Here, we describe the development of a molecular based anode for hydrogen oxidation reaction (HOR) through non-covalent integration of a DuBois type Ni bio-inspired molecular catalyst at the surface of a carbon nanotubes modified gas diffusion layer. This mild immobilization strategy enabled to gain high control over the loading in catalytic sites. Additionally, through the adjustment of the hydration level of the active layer, new record current densities of 214 ± 20 mA cm -2 could be reached at 0.4 V vs RHE with a PGM-free anode, at 25°C. Near-industrially relevant current densities were obtained at 55°C with 150 ± 20 and 395 ± 30 mA cm -2 at 0.1 and 0.4 V overpotential, respectively. These results further demonstrate the relevance of such molecular approaches for the development of electrocatalytic platforms for energy conversion.

How do H2 oxidation molecular catalysts assemble onto carbon nanotube electrodes? A crosstalk between electrochemical and multi-physical characterization techniques

“… 48 These results thus pave the way to the further implementation of such molecular systems into appropriate composite electrode designs to be implemented into functional devices, which should soon allow reaching industrially relevant current and stability performances. 20 …”

“… 18 Briefly, MWNT-a inks were prepared by sonicating MWNT-a in EtOH (3 mg mL −1 ) with or without Nafion (in 1 : 1 ratio with MWNT-a) for 30 minutes in an ultrasonic bath. Then, the dispersion was mixed with a solution of NiArg in milliQ water (4 mM) in a 1 : 3 ratio (30 μL of MWNT-a with 10 μL of NiArg) and 20 μL of the resulting mixture were then deposited directly onto the GDL disk (0.125 cm 2 ) and left to dry for 5 minutes (the drying time had a strong impact on the electrocatalytic performances as previously reported 20 ). The as prepared disk was then directly used for electrochemical measurements in aqueous media.…”

Molecular Catalysts with Diphosphine Ligands Containing Pendant Amines

“…With the use of a related approach, multiwalled carbon nanotubes were modified by using a pyrene butyric acid derivative to create the negatively charged substituents at the electrode surface . These substituents were then equivalently used to electrostatically attract the protonated form of [Ni­(P Cy 2 N Arg 2 ) 2 ] 2+ , yielding a catalytic current of 0.21 A cm –2 with an overpotential of 0.4 V for this anode at 25 °C.…”

“…205 With the use of a related approach, multiwalled carbon nanotubes were modified by using a pyrene butyric acid derivative to create the negatively charged substituents at the electrode surface. 206 These substituents were then equivalently used to electrostatically attract the protonated form of [Ni(P Cy 2 N Arg 2 ) 2 ] 2+ , yielding a catalytic current of 0.21 A cm −2 with an overpotential of 0.4 V for this anode at 25 °C. In additional studies, [Ni(P Cy 2 N Gly 2 ) 2 ] 2+ was tethered to NiO and showed potential for photocatalytic activity as well, 207 and [Ni(P Cy 2 N Gly 2 ) 2 ] 2+ and other derivatives were studied for the impact of ionomers and corresponding mass transport effects, which will be critical for implementation.…”

Non‐Covalent Integration of a [FeFe]‐Hydrogenase Mimic to Multiwalled Carbon Nanotubes for Electrocatalytic Hydrogen Evolution

“…Among the previously reported grafting strategies, immobilization relying on nonspecific physisorption often results in poor electron transfer rates combined with limited stability of the anchoring over long term electrolysis, [56] while covalent coupling typically leads to lower surface loadings, [47,53] inhomogeneous catalyst distribution and possible degradation of the MWNT support [57] . In recent years, non‐covalent integration of metal complexes modified with pyrene units onto π ‐conjugated supports, using π‐π interactions, has been shown to improve catalyst loading and the electronic communication between the complex and the electrode, while providing stable grafting in aqueous catalytic conditions [46,58–65] . To date, this mild surface functionalization strategy has not yet been reported for the anchoring of {(μ‐S 2 )Fe 2 (CO) 6 } derivatives.…”