Electrochemical Behavior of the Palladium-Hydrogen System. I. Potential-Determining Mechanisms

Abstract

The potential of saturated α-palladium in hydrogen-stirred solution compared to a Pt/H2 electrode in the same solution is 0.0495±0.0005 v. The potential-determining reaction on α-palladium is independent of hydrogen pressure. The potential-determining equilibrium is postulated to be, H++e= lim Pd(Pd−H)α. Pure palladium spontaneously absorbs hydrogen in hydrogen-stirred solution until the saturation limit of the α phase is reached. This limiting atomic ratio of H/Pd=0.025±0.005. Between a H/Pd atomic ratio of 0.03 to 0.36 both the α and β phases coexist and the mixed potential is determined by that of the α domains. In the H/Pd region 0.36 to 0.6, the potential is a function of the hydrogen content of the palladium.

Electrocatalytic hydrogenation of acetophenone and benzophenone using palladium electrodes

“…The Pd-hydrogen system is a pseudo-reference electrode [12] and its OCP in the absence of oxygen is fixed by the H + /Pd(H) fast equilibrium and is independent of the hydrogen content in the solid a and b-Pd phases for atomic fraction between 0.03 and 0.36 [12,25,26]. In absence of hydrogen acceptor molecules (such as unsaturated organic molecules or traces of oxygen) at the Pd-H equilibrium potential, the superficial H ads concentration depends on the recombination rate and insertion rate into the Pd lattice.…”

“…In particular, palladium can also absorb hydrogen previously electrosorbed (H ads ), from acid aqueous solutions [11][12][13], which makes it an attractive material for hydrogen storage. In the absence of chemical or electrochemical driving forces, the limited regeneration of H ads is a consequence of its expulsion from the inner metal.…”

Palladium Nanoparticles Supported on Highly Oriented Pyrolytic Graphite: Preparation, Reactivity and Stability

“…The a-PdH x phase, which is stable up to ahydrogen saturation limit of an atomic ratio of H/Pd = 0.025 AE 0.005, shows an OCP of (49.5 AE 0.5) mV in mixtures of hydrogen-saturated sulfuric acida nd sodium sulfate from pH 0.84 to 1.8. [26] When increasing the atomicr atio of H/Pd above 0.025 AE 0.005, the b-PdH x phase is present so that the two phases are in equilibrium up to am aximum H/Pd ratio of about 0.62-0.67, [24] then the PdH x will be in the pure b-phase. The OCP of pure bPdH x is at 0V .W ith aH /Pd atomicr atio of 0.03 to 0.36, both the a and b phases coexist and the OCP is determined by that of the a domains.…”

“…RHE. [26] ChemElectroChem 2015, 2,547 -558 www.chemelectrochem.org may,i np art, be attributed to structural parameters such as the density of low coordinated atoms, steps and defects, which are sensitivet ot he particles ize. The spillover effect of hydrogen from Pd to HOPG should also be considered, because this effect is sensitive to the interparticle distance, which becomes larger when the NPs are smaller.…”

“…For aH /Pd ratio of between 0.36 and0 .67, the potentiali safunction of the hydrogen content of the Pd. [26] In the HER experiments, ap otentials weep in the cathodic directionwas applied to the workinge lectrode. An electrocatalyticallyp romoted hydrogen absorption proceeds on the Pd before or during the evolutiono fh ydrogen molecules.T he absorptionr ate of hydrogen into the Pd bulk is controlled by diffusion of hydrogen atoms.…”