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The present study focuses on the electrolysis of kraft black liquor (BL) for energy and lignin recovery. The concept has economic and environmental advantages, as it simultaneously generates a clean fuel gas (hydrogen) at the cathode and a solid with economic value (lignin) at the anode. Platinum (Pt), nickel (Ni), and AISI 304 stainless steel (SS) are assessed as potential anodes and cathodes for the BL electrolysis. Voltammetric methods are used to study the lignin oxidation in the BL, allowing the calculation of the charge transfer coefficient and the number of exchanged electrons. The hydrogen evolution reaction (HER) in BL is also evaluated in the same electrodes, with the Tafel slopes, charge transfer coefficients and exchange current densities being determined. Pt leads to the best results for both HER and lignin oxidation, followed by Ni, whereas AISI 304 SS is not appropriate. A small-scale laboratory BL electrolyzer using Ni plate electrodes is assembled and tested. The lignin electrodeposited at the anode is characterized by Fourier Transform Mid Infrared Spectroscopy and compared with lyophilized lignin and Klason lignin. The higher purity of the lignin obtained by BL electrolysis suggests further work on the development of this new technology.

Black liquor is a pulp mill effluent from wood cooking with a solid content of 15-18 wt.%, which is mostly lignin. The present study focuses the electrolysis of black liquor for energy recovery. The process has several economic and environmental advantages, as it simultaneously generates a clean fuel (hydrogen) at the cathode and a precipitated material with economic value (lignin) at the anode surface. Platinum, nickel, and AISI 304 stainless steel bulk electrodes are tested for black liquor electrolysis, both as anodes and as cathodes. Voltammetric methods are used to study the lignin oxidation in the black liquor at room temperature, allowing the calculation of kinetic parameters such as the charge transfer coefficient and the number of exchanged electrons. The hydrogen evolution reaction in the black liquor is also evaluated. A small-scale laboratory black liquor electrolyzer using Ni plates is assembled and its operation parameters are evaluated.

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The synthesis of palladium-based trimetallic catalysts via a facile and scalable synthesis procedure was shown to yield highly promising materials for borohydride-based fuel cells, which are attractive for use in compact environments. This, thereby, provides a route to more environmentally friendly energy storage and generation systems. Carbon-supported trimetallic catalysts were herein prepared by three different routes: using a NaBH4-ethylene glycol complex (PdAuNi/CSBEG), a NaBH4-2-propanol complex (PdAuNi/CSBIPA), and a three-step route (PdAuNi/C3-step). Notably, PdAuNi/CSBIPA yielded highly dispersed trimetallic alloy particles, as determined by XRD, EDX, ICP-OES, XPS, and TEM. The activity of the catalysts for borohydride oxidation reaction was assessed by cyclic voltammetry and RDE-based procedures, with results referenced to a Pd/C catalyst. A number of exchanged electrons close to eight was obtained for PdAuNi/C3-step and PdAuNi/CSBIPA (7.4 and 7.1, respectively), while the others, PdAuNi/CSBEG and Pd/CSBIPA, presented lower values, 2.8 and 1.2, respectively. A direct borohydride-peroxide fuel cell employing PdAuNi/CSBIPA catalyst in the anode attained a power density of 47.5 mW cm−2 at room temperature, while the elevation of temperature to 75 °C led to an approximately four-fold increase in power density to 175 mW cm−2. Trimetallic catalysts prepared via this synthesis route have significant potential for future development.

The present work combines the advantages of using highly active Pt together with low cost transition metals, like Co, Ni, and Cu, in bimetallic alloy nanoparticles along with the employment of reduced graphene oxide (rGO) as an efficient carbon-based electrocatalyst support. Thus, Pt and three different MPt (M = Ni, Co, Cu) alloy nanoparticles supported on rGO were synthesized, characterized (by TEM and ICP-MS), and assessed as electrocatalysts for hydrogen production by alkaline water electrolysis. The evaluation of HER kinetics at the MPt/rGO composites was done by linear scan voltammetry measurements in 8 M KOH solution. Higher current densities were achieved for the MPt/rGO electrocatalysts (in comparison with the monometallic one, Pt/rGO), with considerably lower Tafel slopes. It was observed that increasing the temperature up to 338 K leads to a substantial increase of HER current densities at all electrocatalysts. The corresponding Arrhenius analysis showed that HER activation energies in the rGO-supported electrocatalysts ranged between 27.5 and 36.7 kJ mol-1.