Main activities and results 2017

WP 2: Functionalization of the 3D metallic nanofoams

Task 2.2 – Functional electrodes for hydrogen production       Objective:  surface  functionalization for H2 production through: (i) deposition of Pd /Pt clusters by electroless or electrochemical routes onto  Ni and Ni alloy foams; (ii) formation of porous Ni(OH)2  surfaces by oxidising the metallic Ni foams  structures; (iii) formation  of  polpyrrole  (PPy)  clustered  films  onto  the  Ni  and  Ni alloys foams

Pd/Pt surface functionalisation of  porous Ni  and Ni-Mo alloy structures

SEM micrographs of Ni-Pd alloy foam (1 wt. % Pd) electrodeposited at 25oC for 3 min. (c.d. = 1 A/cm2) and EDX maps showing the distribution profiles of elements within the deposited alloy
The addition of PdCl2 in the electroforming electrolyte facilitates the co-deposition of Pd, while keeping the porous morphology of genuine Ni foam. Pd element is quite uniformly distributed within the alloy deposit. Usually the Pd content was in the range of 0.3-3 wt.% with higher values on the increase of Pd concentration in the electrolyte or of the applied current density.
EDX maps showing the distribution profiles of elements for Ni-Mo alloy electrodeposited onto NiPdf
(0.5 % Pd) at 60oC for 20 min. (c.d = 4 A/dm2)
EDX maps showing the distribution profiles of elements for Pt functionalized 3D Nif substrate (0.2 wt.% Pt) obtained by electrochemical deposition (90oC, 6.5 A dm-2, 5 min.)

Formation of porous Ni(OH)2  surfaces

Formation  of  polpyrrole  (PPy)  clustered  films  onto  the  Ni  and  Ni alloys foams

SEM micrographs of PPy layer onto Nif (a,b) and NiW/Nif obtained through electrochemical polymerization involving 0.1M pyrrole in 0.5M H2SO4

WP 5 – Electrochemical performance of metallic nanofoams as electrodes for hydrogen production

Comparative linear polarization curves of HER in seawater for different systems of Pd functionalized Ni foams (a), NiMo/ Ni foams (b) and of Pt functionalized Ni foams (c)

The HER activity of Nif may be enhanced through Pd surface modification. The corresponding Tafel slopes for NiPdf and Pdchem/Nif are of 123 and 120 mV.dec-1, respectively, suggesting that the HER process obeys Volmer reaction mechanism. The higher value of Nif may be related to the presence of oxides films on the surface.  The Pd functionalization of Ni-Mo alloy based systems determines only a slight improvement of the catalytic activity. The significant effect is mainly due to the presence of Mo as alloying element. The determined Tafel slope values ranged from 118 to 105 mV.dec-1, indicating the Volmer step as rate determining step.

Pt surface modification provides moderate performance against HER as compared to Pd in the case of seawater electrolyte. However Pt improved the HER activity when 1M KOH  alkaline electrolyte has been involved, materialized by exchange current values of one order of magnitude higher.