Improving the intrinsic activity of electrocatalysts for sustainable energy conversion: where are we and where can we go?

As we are in the midst of a climate crisis, there is an urgent need to transition to the sustainable production of fuels and chemicals. A promising strategy towards this transition is to use renewable energy for the electrochemical conversion of abundant molecules present in the earth''s atmosphere such as H₂O, O₂, N₂ and CO₂, to synthetic fuels and chemicals. A cornerstone to this strategy is the development of earth abundant electrocatalysts with high intrinsic activity towards the desired products. In this perspective, we discuss the importance and challenges involved in the estimation of intrinsic activity both from the experimental and theoretical front. Through a thorough analysis of published data, we find that only modest improvements in intrinsic activity of electrocatalysts have been achieved in the past two decades which necessitates the need for a paradigm shift in electrocatalyst design. To this end, we highlight opportunities offered by tuning three components of the electrochemical environment: cations, buffering anions and the electrolyte pH. These components can significantly alter catalytic activity as demonstrated using several examples, and bring us a step closer towards complete system level optimization of electrochemical routes to sustainable energy conversion.

We evaluate the improvements over the past two decades in intrinsic activity of electrocatalysts for sustainable energy conversion, and highlight opportunities from tuning the electrolyte.     

Individual variations in the correlation between erythemal threshold, UV-induced DNA damage and sun-burn cell formation.

A linear correlation between erythema intensity and DNA damage upon exposure to UV has not been firmly established. Many of the deleterious effects of UV exposure do occur after exposure to suberythemal doses. After DNA damage, cells undergo DNA repair. It is commonly accepted that when the burden of damage is beyond the repair capacities, the cell undergoes programmed cell death or apoptosis. The aim of this study is to quantify the amount of UV-induced DNA damage (estimated via the measurement of DNA repair or unscheduled DNA synthesis or UDS) and cellular damage (estimated via the determination of the density of sunburn cells or SBC). If DNA damage and erythema are correlated, similar intensity of UDS and similar density of SBC should be found in volunteers irradiated with a UV dose equal to two minimal erythema doses (MED). Our results show that in 15 different individuals the same relative dose (2 MEDs) provokes UDS values, which vary within a factor of 4. An even larger variability affects SBC counts after the same relative dose. When DNA damage or SBC are plotted versus the absolute dose (i.e. the dose expressed in J/m(2)), there is a rough correlation (with several exceptions) between dose and extent of UDS and SBC counts. It seems possible to divide the volunteers into two subpopulations with different susceptibilities to UV damage. It is well known that UDS and SBC measurements are often affected by large experimental indeterminacy, yet, the analysis of our results makes it plausible to suggest that for the triggering of erythema, a common threshold value for DNA damage or for SBC count are not to be found. In conclusion, the erythema response seems to be loosely correlated with DNA damage. This suggests that the protection offered by the sunscreens against DNA damage, the molecular basis of UV-induced mutagenesis, might not be related to the sun protection factor (SPF) indicated on the label of sunscreens, which is evaluated using the erythema as an endpoint.     

Evaluation of a new maintenance concept for the preservation of highways

Asphalt roads gradually deteriorate over time and need mendingto remain in a good state. Inspections are performed to obtaininformation about the current state of the road; when the levelof damage reaches the established standards, the road is repairedthrough a maintenance action that is considered most cost-effective.Because of economies of scale, it is to a certain extent economicalto limit the number of maintenance services by integrating neighbouringsegments into a homogeneous section which is completely repaired.In this report we consider the question of whether it is economicallyjustified to adopt a maintenance concept in which the road isoccasionally regenerated from junction to junction with a distanceof several kilometers. The big advantage of junction-to-junctionmaintenance is that it can be done within special road barrierconstructions which reduce the road capacity only slightly,so that the road can be maintained 24 hours a day.     

Nuclear charge radii of neutron-deficient lead isotopes beyond N = 104 midshell investigated by in-source laser spectroscopy

The shape of exotic even-mass (182-190)Pb isotopes was probed by measurement of optical isotope shifts providing mean square charge radii (delta(r(2))). The experiment was carried out at the isolde (cern) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of delta(r(2)) to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic Z=82 lead isotopes near neutron midshell (N=104).     

Generator-coordinate study of inelastic α + 12C scattering

A multi-channel calculation performed with the generator coordinate method is presented for α + ¹²C scattering. The inelastic channel α + ¹²C(2⁺) is included. Bound-state and resonance energies are determined for J^π = 0⁺ up to 6⁺. For the negative parity levels, the results are very similar to those obtained with a single-channel calculation. The positive parity resonances are more numerous and in better qualitative agreement with experiment in the multi-channel calculation. However, an incorrect value for the threshold energy α + ¹²C(2⁺) channel prevents one from obtaining a quantitative agreement with experiment.     

Evolution of Concentrated Vortices in a Viscous Fluid

Evolution of the vortices of monopole and dipole types in a viscous fluid is considered numerically. Theory and numerical results are compared for some particular exact solutions. A good agreement is obtained for the dipole vortices (viscous Chaplygin-Lamb vortices) moving with variable velocities due to viscosity. For the monopole type vortices, the agreement is more or less good only at an initial stage of their evolution; while in the long-lime asymptotics the law of vorticity decay other than the theoretical one is discovered. The reason for such a discrepancy is discussed. The interactions of dipole vortices with each other and with rigid boundaries are studied too. The stability of dipole vortices with complex internal structures is considered briefly.     

Adiabatic time-dependent Hartree-Fock calculation of fusion cross sections: Application to 40Ca-40Ca

Using the adiabatic time-dependent Hartree-Fock method we calculate the interaction and inertial mass parameter relevant for a heavy-ion collision. In this work, which extends an earlier study for lighter systems, we investigate the case of ⁴⁰Ca-⁴⁰Ca for which detailed experimental information is available. As already found for lighter colliding ions, the mass parameter exhibits a large peak for interdistances slightly smaller than the barrier radius. We use our results to evaluate the fusion cross section and we find that the structure in the inertial mass brings the theoretical cross section in close agreement with data.     

Classical spin variables and classical counterpart of the Dirac-Feynman-Gell-Mann equation

In an extended relativistic fluid droplet, it is possible to define new internal variables which correspond to the classical counterpart of spin. If we introduce a new constraint, different from Weysenhoff's, we obtain by quantisation the Feynman-Gell-Mann wave equation. This also yields a theoretical connection between mass and spin which can be compared with the observed baryon boson mass spectrum.