Abstract
High investment costs and a dependence on noble metal catalysts currently obstruct the large-scale implementation of proton exchange membrane water electrolyzers (PEMWEs) for converting fluctuating green electricity into chemical energy via water splitting. In this context, this work presents a high-performing and stable non-noble metal catalyst for the hydrogen evolution reaction (HER), consisting of [Mo3 S13 ]2- clusters supported on nitrogen doped carbon nanotubes (NCNTs). Strikingly, a significant electrochemically induced activation of the Mo3 S13 -NCNT catalyst at high current densities is observed in full cell configuration, enabling a remarkable current density of 4Acm-2 at a cell voltage of 2.36V. To the authors' knowledge, this is the highest reported value to date for a PEMWE full cell using a non-noble metal HER catalyst. Furthermore, only a minor degradation of 83µVh-1 is observed during a stability test of 100h constant current at 1Acm-2 , with a nearly unchanged polarization behavior after the current hold. Catalyst stability and activity are additionally analyzed via online dissolution measurements. X-ray photoelectron spectroscopy examination of the catalyst before and after electrochemical application reveals a correlation between the electrochemical activation occurring via electrodissolution with changes in the molecular structure of the Mo3 S13 -NCNT catalyst.
Highlights
X-ray photoelectron spectroscopy examination of the catalyst before and after electrochemical application reveals a correlation between the electrochemical activation occurring via electrodissolution though the costs for catalyst only account for ≈8% of a PEMWE stack and ≈5% of the overall PEMWE system costs, the limited availability of platinum group metals (PGMs) could hinder the implementation of PEMWE on a terawatt with changes in the molecular structure of the Mo3S13-NCNT catalyst
Using surplus electricity from fluctuating renewable energy and the hydrogen evolution reaction (HER) on the cathode side, sources to generate hydrogen via water electrolysis combined numerous reports exist targeting the reduction of PGMs in the with hydrogen storage could play a key role in the transition catalyst layer.[9,12]
[Mo3S13]2− clusters and Mo3S13-NCNT hybrid were synthesized as described in the Experimental Section
Summary
The doublet peak is attributed to Mo with +4 oxidation state, occurring in MoIV(S–S)3(μS) structures, where (S–S)2− and μS units are assigned for bridging disulfide and apical sulfide, respectively.[30,32] The additional small doublet peaks at 236 and 233 eV in the Mo3d spectra of Mo3S13-NCNT hybrid (Figure 2c) can be ascribed to MoO3 byproducts arising from DMF treatment, absent in the Mo3d region of the pristine [Mo3S13]2− clusters (Figure 2b). This explains for the lower S/Mo ratio of Mo3S13-NCNT compared to [Mo3S13]2− as mentioned above. [Mo3S13]2− clusters powder exhibited Raman spectrum with a distinct finger-print from 200–600 cm−1 (Figure S1, Supporting Information), which was consistent with previous reports.[30,32] Overall, the successful anchoring of [Mo3S13]2− onto NCNTs as well as the almost unaltered stoichiometry of the nanocluster structure are demonstrated for both freestanding [Mo3S13]2− clusters and in Mo3S13-NCNT hybrid in agreement with previous works.[30,32]
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