Multi-decadal shoreline changes in Eastern Ghana—natural dynamics versus human interventions

Human infrastructures, such as dams, seawalls, and ports, can affect both the sedimentary budget and nearshore hydrodynamics, enhancing and accelerating the loss or gain of coastal sediments. Understanding the processes and factors controlling beach morphodynamics is essential for implementing adequate adaptation strategies in coastal areas, particularly in those regions where coastal protection measures are scarce. This study analyzes shoreline changes in the Keta Municipal District, located in southeastern Ghana (West Africa). This area is characterized by the sedimentary input of the Volta River, forming a river delta situated to the west, i.e., updrift, of our study site. Following the construction of two dams (Akosombo and Kpong) on the Volta River in 1965 and 1982, groins and revetments have been built along the coast between 2005 and 2015 to reduce the high rates of coastal erosion in this area. Here, we explore the influence of these dams and the hard protection constructions on beach morphodynamics using historical maps and satellite images complemented by a shoreline survey undertaken with a differential GNSS in 2015. The multi-decadal evolution between 1913 and 2015 reconstructed for 90 km of shoreline suggests that local erosion rates in the region predate the construction of the two dams on the Volta River, indicating that these structures might not be the primary driver of coastal erosion in this area, as previously suggested. We emphasize that delta dynamics under conditions of high-energy longshore drift, modified by anthropogenic drivers such as sand mining, play a key role in the long-term evolution of this coast. Our results also show that the infrastructures built to halt coastal erosion result in localized erosion and accretion down-current along the coastline towards the border with Togo, highlighting the need for a transnational perspective in addressing the problems caused by coastal erosion

Enhancing oxygen evolution functionality through anodization and nitridation of compositionally complex alloy

Compositionally complex materials (CCMs) have recently attracted great interest in electrocatalytic applications. To date, very few materials were systematically developed and tested due to the highly difficult preparation of high-surface-area CCMs. In this work, a surface of a compositionally complex FeCoNiCuZn alloy (CCA) was nitridated with subsequent anodization leading to morphological and compositional modifications. Notably, the electrochemical surface area and surface roughness as well as the electrocatalytic activity of the anodized material exhibit significant enhancement. Oxygen evolution reaction (OER) activity by the anodized CCN (CCN–AO) proceeds with remarkably small overpotential (233 mV) at 10 mA cm−2 in 1 M KOH. Experimental characterization indicates that the oxidation state of Co plays a critical role in the Fe–Co–Ni electrocatalyst. The developed approach and design strategy open up immense prospects in the preparation of a new, affordable, scalable and effective type of complex and high-performance electrocatalytic electrodes with tunable properties

Control of growth kinetics during remote epitaxy of complex oxides on graphene by pulsed laser deposition

Remote epitaxy through 2D materials opens new opportunities for research and application, overcoming some limitations of classical epitaxy and allowing the creation of freestanding layers. However, using graphene as a 2D interlayer for remote epitaxy of metal oxides is challenging, particularly when carried out by pulsed laser deposition (PLD). The graphene layer can be easily oxidized under the typically applied high oxygen pressures, and the impact of highly kinetic particles of the plasma plume can lead to severe damages. In this study, both aspects are addressed: Argon is introduced as an inert background gas in order to avoid oxidation and to reduce the kinetic impact of the plasma species on graphene. The laser spot size is minimized to control the plasma plume and particle flux. As a model system, strontium titanate (STO) is quasi-homoepitaxially grown on graphene buffered STO single crystals. Raman spectroscopy is performed to evaluate the 2D, G, and D band fingerprints of the graphene layer and to assess the defect structure of the interlayer after the deposition. Our results prove that control of the growth kinetics by reducing the laser spot size and by using high argon pressures provides a key strategy to conserve graphene with a low defect density during PLD while allowing a layer-by-layer growth of structurally coherent oxide layers. This strategy may be generalized for the PLD remote epitaxy of many complex oxides, opening the way for integrating 2D materials with complex oxides using widely accessible PLD processes