Pedals with largest outside platform area I am 86 years of age with RA and badly splayed out feet. I already have pedal extenders on my custom 350 watt ebike trike (on a Biria frame) and have wrapped rug/carpet laying  tape around the pedals with the rough gritty surface up - to no avail. 

I have tried Amazon and eBay and can't identify a wide platform bike pedal that might solve my problem. Does any body out there have a solution or recommendation. Be an angel. Mike Crombie
Something like the Crank Bros Stamp pedals might work. The large version are recommended for people with size 10-15 feet, and they also have metal pins that stick out allowing your shoe to grip onto the pedal better. 

It might make sense to go to a local bike shop to see what help they can give you. Seeing the pedals in person might let you know if they can work. Or they might be able connect you with someone in your area that modifies bicycles for people with mobility issues.