Electric cars are in the spotlight. Post-Dieselgate, many consumers think it is only a matter of time before clean green vehicles become the norm and the guilt of transport emissions becomes a thing of the past. But ethical question marks loom large above the mining conditions of cobalt - a mineral used in the lithium-ion batteries that power cars, as well as our smartphones and laptops.
More than half of global supplies hail from one of the world's poorest nations, the Democratic Republic of Congo (DRC), where corruption abounds and children toil.
"Working conditions are appalling, there is no safety equipment and people risk getting buried alive in hand-made mines,” Matt Dummett, a researcher at Amnesty International, told DW. "I've seen children as young as seven working on the surface, collecting stones and facing brutality and intimidation during long days in the heat."
In the past few years, human rights campaigns and investigative media reports have sought to shine a light on the murky cobalt trade, especially on so-called artisanal mines where men tunnel deep into the earth using basic hand tools while others - including women and children - lug heavy bags of rocks from which the cobalt is extracted.
The World Bank estimates two thirds of Congolese people live on less than 0.86 euros ($1.90) a day and Amnesty says hunger and unemployment often drive people to hunt for valuable minerals.
And there is no shortage of buyers for whatever they find. As carmakers, including VW and Daimler, where electric vehicles are expected to make up a quarter of sales by 2025, accelerate towards a cleaner future, and as engineers fine-tune new designs to compete with the likes of Tesla, they boost competition for raw materials.
Volkswagen recently launched a tender to secure cobalt supplies for at least the next five years - following similar efforts by BMW and Tesla Motors - and overall demand for the mineral is forecast to jump eleven-fold by 2025.
This will further inflate prices, which have risen sharply over the past year. It will also focus attention on mining practices.
"Cobalt is no longer an obscure mineral. Today it is very possible to follow the paper trail,” Dummett said. "These days, companies have no excuse.”
To their credit, some western firms have joined pan-industry moves towards good-practice guidelines, including the Responsible Cobalt Initiative.
But human rights watchdogs remain on alert. "This could be really good," Dummett continued, "or maybe companies think that by signing up to these initiatives they are off the hook.”
Last month the BMW group said it was working to make its cobalt supply chain more transparent by ensuring public access to information relating to its sources and smelters. Spokesperson for sustainability Kai Zöbelein told DW that BMW adhered to strict rules.
"For five years we have been continually analysing and tracking our cobalt supply chains,” he said.
"Smelters in our chain use cobalt from DRC but only from large-scale mines,” he added, distancing the car giant from unregulated small-scale artisanal production.
A VW spokesperson said it does not directly purchase cobalt, but sources batteries from suppliers, and investigates reports of violations "immediately and thoroughly.”
Sourcing cobalt from third parties and buying minerals from DRC's industrial mines does not, however, necessarily mean international firms are dealing ethically, particularly given the country's corruption rating.
Research by non-profit Global Witness reveals that between 2013 and 2015 more than 647 million euros in mining revenues paid by companies to Congolese state bodies was lost to the treasury.
Many Congolese mining licences are sold by Gecamines, the state mining company, which Global Witness researcher Peter Jones calls a "black hole”.
"Gecamines is headed by one of [President Joseph] Kabila's inner circle. It has repeatedly sold off stakes in its mining projects, it doesn't publish its accounts and there is no way of knowing where exactly money paid into it could end up,” Jones said.
And with Kabila, whose second term expired last December, holding back on setting a date for fresh elections, the potential for corruption remains high.
Pro-electric mobility think tank Agora Verkehrswende says due diligence and rigorous checks throughout the supply chains are imperatives if poor ethical standards are to be kept out of the next generation of clean vehicles. In a recent report, director Christian Hochfeld cited existing standards for so-called conflict minerals such as gold as examples to follow.
He also urged more recycling of old batteries to maximise the use of cobalt already mined.
"Ambitious environmental and social standards are an essential prerequisite for the growing acceptance of electro-mobility,” Hochfeld said. "Not least because it needs to be credible as an environmental, climate friendly technology.”